The Right Water Temperature in Hydroponics: 18 to 22 °C

Hydroponics knowledge

18 to 22 °C: the comfort zone for your roots

Why water temperature matters so much, what happens with water that is too cold or too warm, and how I keep the water warm in winter and cool in summer. With my values from the book.

🥶

Below 18 °C: too cold

roots work more slowly, the plant grows slowly

✅

18 to 22 °C: good

ideal for most hydroponic crops

👌

Up to 24 °C: still fine

now keep an eye on the temperature

🔥

From 25 °C: too warm

air stone, shade, sheltered spot

Contents

🌱Nutrient uptake 🌡️The perfect temperature 🔥Too warm 🥶Too cold 🛠️Keeping the temperature stable ☀️Heat checklist 📏Measure instead of guess 💬FAQ

The right water temperature is crucial for the success of your hydroponic setup. It affects plant growth and nutrient uptake. Find out which temperatures are optimal, what effects deviations have and how to control the temperature effectively. If you have questions, I am happy to help you create optimal conditions together. The quickest way to reach me is via WhatsApp.

🌱Basics

Influence of water temperature on nutrient uptake in hydroponics

Water temperature is a crucial factor in Hydroponics, growing plants in water-based solutions instead of soil. In this system, plants are supplied with everything they need for growth directly via the water. Water temperature plays a central role, because it affects not only the plants‘ nutrient uptake but also the microbial environment and the oxygen content of the water. An optimal water temperature promotes plant growth, strengthens root health and minimises the risk of disease. Temperatures that are too high or too low, however, can cause various problems, from slowed growth to root rot.

That is why it is essential for hydroponics enthusiasts and professionals alike to have a deep understanding of the importance of water temperature and the challenges that come with it.

Why water temperature matters so much

In hydroponics your plants get everything via the water: nutrients, water and also oxygen for the roots. Water temperature is often underestimated. It helps decide how well the roots work, how much oxygen is in the water and how quickly pathogens multiply.

My rule of thumb

EC, pH and water temperature belong together. If a plant has problems, I always check all three. Often EC and pH are fine and the plant still grows poorly. Then the water is usually too cold or too warm.

Roots breathe day and night

Roots do not photosynthesise. They take their oxygen from the water and breathe around the clock, including at night. Only with enough oxygen do they stay healthy and can take up nutrients. And this is where temperature comes in: the warmer the water, the less oxygen it can hold.

Oxygen in water at full saturation

Water temperature	Oxygen in water, at most about
15 °C	10.1 mg per litre
20 °C	9.1 mg per litre
25 °C	8.3 mg per litre
30 °C	7.6 mg per litre

These are values for pure water at full saturation, as given in technical tables. At the same time, roots breathe harder in warmth and need more oxygen. So less supply meets more demand. From about 25 °C it gets tight.

📖Why warm water robs the roots of oxygen, I explain in my book in the chapters “Wassertemperatur” (Water temperature) and “Sauerstoff im Wasser” (Oxygen in water). Just check the table of contents.›

🌡️Target values

The perfect water temperature

The optimal water temperature is crucial for the success of your hydroponic system. For most hydroponic plants the ideal water temperature is between 18 and 22 degrees Celsius. In this range the plants can efficiently take up nutrients and use oxygen from the water.

below 18 °C

too cold

18 to 22 °C

ideal

up to 24 °C

still good

from 25 °C

too warm

Too warm

Less oxygen

Temperatures that are too warm can reduce the oxygen content of the water, which can suffocate the plant roots.

Too cold

Slow metabolism

Temperatures that are too cold, on the other hand, slow down the plants‘ metabolism, leading to slow growth and poor health.

It is important to consider the specific requirements of your plant species. Some plants prefer slightly warmer or cooler water, so it is advisable to research the ideal conditions for each plant and use heating or cooling systems if necessary to maintain the optimal water temperature.

My values for water temperature

Water temperature	What it means	What I do
below 18 °C	too cold: roots work more slowly, less nutrient uptake	help out with a heater in winter
18 to 22 °C	good: the comfort zone for the roots	nothing, just measure regularly
up to 24 °C	still fine	let the air stone run, shade the tank
from 25 °C	too warm: little oxygen, root rot develops faster	air stone is a must, cool the tank

Ideal

18 to 22 °C

Still good

up to 24 °C

Too warm

from 25 °C

Tomatoes

18 to 24 °C

For most hydroponic crops the range of 18 to 22 °C is ideal. Specialist sources from commercial growing give very similar values for the root zone. For my tomatoes in the tomato tower I keep the water at 18 to 24 °C, and the air stone always runs there.

📖My values for water temperature are in my book in the chapter “Wassertemperatur” (Water temperature), the values for tomatoes in the chapter “Dein Sommer-Rhythmus” (Your summer rhythm). Just check the table of contents.›

Free

Which tower suits you?

A few questions about space, location and what you want to harvest, and you get a recommendation.

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🔥Too warm

Water temperature too high in the hydroponic system

Water temperature in hydroponic systems plays a crucial role in the growth and health of plants. An inappropriate water temperature can bring various risks:

Too warm: from 25 °C. The more common problem in summer.

Warm water holds less oxygen. Stress for the roots increases, and root rot can develop faster. In summer especially I therefore check the water temperature regularly, because a tank in the sun heats up quickly.

Lack of oxygen

Warm water can absorb and hold less oxygen than cold water. A lack of oxygen can cause the plant roots to suffocate and rot. That is why on hot days it is necessary to support the roots with an air stone. Outdoors from a water temperature of 25 °C it is a must, and indoors it can also run in the tower.

An air stone is the most important help with warm water. It does not lower the temperature, but it constantly brings fresh oxygen into the water. It does not go on the timer but straight into the socket. That way it also runs at night, when the roots breathe just as much.

Where	Air pump	Why
Seedling station	continuously, day and night	the roots hang in standing water
HydroFlex Tower indoors	can, does not have to	the trickling water picks up air
outdoors from 25 °C water temperature	must	warm water holds less oxygen
DWC and Kratky with aeration	always, continuously	the roots stand in the nutrient solution
Tomato tower	always, each container its own	the roots hang directly in the nutrient solution

Air pump set 10 W with manifold, hose and 4 air stones

This is my powerful air pump that supplies 4 systems with oxygen at the same time. Complete with air manifold, hose and 4 air stones.

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Solar air pump 2.5 W with battery

It also works without mains power and is enough for two systems. The solar air pump has a battery and keeps running at night.

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Angebot

Strong air pump for many containers

The stronger air pump for many containers, so even warm water has enough oxygen.

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Increased algae growth

At higher temperatures algae can grow faster in hydroponic systems, but only if light gets into the container. Light is what matters, not warmth. Algae use up nutrients and oxygen that should benefit the plants and can suffocate the roots.

Algae mainly need light. I have no problems with algae even above 30 °C: my container is closed and hardly any light gets in. On top of that the air stone runs, always in warm weather. That also keeps the roots healthy. You can read more about this under Algae.

3 % hydrogen peroxide against algae and pathogens such as bacteria: only for cleaning the empty system

To fight algae and bacteria in your hydroponic setup, you can clean the empty system with 3 % hydrogen peroxide (H₂O₂). For cleaning, the dosage is about 3 to 5 ml of hydrogen peroxide per litre of water. It does not belong in the nutrient solution with the plants.

Important notes on use:

Dosage: use 3 to 5 ml of 3 % hydrogen peroxide per litre of water, in the empty system without plants.
Hazard warning: Hydrogen peroxide can damage your plants‘ roots, even in small amounts in the nutrient solution. So make sure not to exceed the dosage, distribute the hydrogen peroxide evenly in the water and only add it to the empty system.
Application: Add the hydrogen peroxide slowly to the water in the empty container to ensure even distribution, and let the pump run briefly so it also reaches the hoses and segments. Then rinse everything thoroughly with clean water before the plants go back in. With correct use you can fight algae and bacteria effectively while protecting the health of your plants.

Only for cleaning: Hydrogen peroxide does not go into the running nutrient solution with your plants. In a study with lettuce in hydroponics (Horticulturae 2021), plants with mineral fertiliser grew poorly or died at just 37.5 to 75 mg per litre. 3 to 5 ml of the 3 % solution per litre is 90 to 150 mg. Against algae during operation, a dark, closed container helps.

3 % hydrogen peroxide for cleaning

For cleaning the empty system against algae and bacteria. Then rinse thoroughly with clean water.

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Dosing syringe set

Ideal for precisely dosing fertiliser and hydrogen peroxide.

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Measuring cups with lid

These cups with lids are extremely handy. If you can no longer reach a half-empty fertiliser mix with the syringe, this cup is ideal. It can be closed tightly, so you can add some water and mix all three fertilisers in it. Then you add the nutrients to the water and have everything prepared cleanly and efficiently.

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Pathogens

Some harmful bacteria and fungi can multiply faster at higher water temperatures. This can lead to root diseases such as root rot, which can weaken or kill the plants.

Root rot

Healthy roots are white or pale and strong. Rotten roots are brown, slimy and smell musty. The cause is usually water above 24 °C, light or dirt in the container, or too much fertiliser. Pathogens such as Pythium like warm, oxygen-poor water, which is why root rot is more common in summer.

If it has caught you, cut off the brown roots, clean the container, mix fresh nutrient solution and let the air stone run. Also provide plenty of air movement. Lots of white roots are a good sign; never cut those off. With an air stone root rot hardly ever occurs for me, even at 38 to 39 °C in my greenhouse.

📖What I do about root rot is in my book in the chapter “Probleme lösen” (Solving problems) under “Wurzelfäule” (Root rot). Just check the table of contents.›

Stress for the plants

Water that is too warm can stress the plants, which affects their growth and development. This often leads to weaker plants with lower yields.

It is therefore important to keep an eye on the water temperature and take measures to prevent overheating. These measures include using water chillers, insulating the water tank and ensuring good ventilation of the growing room.

From my shop

Everything for your soil-free start

HydroFlex Tower for indoors and outdoors, seedling box, seedling station, support rings and my own nutrient. After you buy, I’ll help you on WhatsApp.

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🥶Too cold

Water temperature too low in the hydroponic system

Low water temperatures can be just as problematic for hydroponic systems as temperatures that are too high. Here are the main problems caused by water that is too cold:

Too cold: below 18 °C. No drama, but the plants grow more slowly.

If the water is too cold, the roots work more slowly. The plant takes up fewer nutrients and grows slowly, even if EC and pH are right. In winter the water cools down quickly, for example in an unheated room. In winter my meter has shown 17 °C before. That is no drama yet, but already a little cooler than my comfort zone.

Risk

Slow growth

Cold water slows down the plants‘ metabolic processes, because enzymatic activity depends on temperature. This leads to slower growth overall and a longer time to harvest.

Risk

Root damage

Extremely cold water temperatures can cause physical damage to the roots. The roots become less efficient at taking up water and nutrients, which can lead to growth disorders and disease.

Risk

Impaired nutrient uptake

Low temperatures can hinder the uptake of certain nutrients. Nutrients such as phosphorus and potassium in particular are taken up less efficiently at colder temperatures, which can lead to deficiency symptoms.

Risk

Increased susceptibility to disease

Cold water can weaken the plants‘ defences because the roots work more slowly, making them more susceptible to diseases and pests. But root rot develops much more often in warm, oxygen-poor water above 24 °C.

Good to know

Dark, purple-tinged leaves indicate phosphorus deficiency. It often occurs with cold water, even though there is enough phosphorus in the nutrient solution. The roots simply take it up less well in the cold.

Mottled leaves in spring

In spring the leaves sometimes discolour or become mottled. That is due to the water temperature: at night the nutrient solution is often only 11 to 12 °C, and then the roots do not take up all nutrients. If the leaves discolour in May, it is usually the cold water and not the fertiliser. So do not add more fertiliser. As soon as it gets warmer, everything recovers and grows back wonderfully.

To avoid these problems, it is important to keep the water temperature constantly within an optimal range. This can be achieved by using water heaters, insulating the water tank and controlling the room temperature.

How to keep the water warm

In winter I keep the water constantly at 18 to 20 °C with an aquarium heater. It has a thermostat and switches itself off when the set temperature is reached. To keep its electricity use low, wrap the container well, for example in polystyrene. That way little heat is lost.

Water temperature also matters when moving outdoors. The water should be between 18 and 22 °C, roughly room temperature. That is why I only move the tower outdoors from mid-May. Before that the water cools down too much at night.

My own nutrient

Frankie’s liquid nutrient

Seedling and leaf nutrient from one bottle, with calcium and magnesium, made for soft water. For all plants from sowing to the growth phase, leafy plants until harvest.

View in the shop ›

🛠️Keep it stable

Stabilising the water temperature

The right water temperature is crucial for plant growth and health in a hydroponic system. Here are various methods to regulate the water temperature effectively and keep it in the ideal range of 18 to 22 degrees Celsius:

How I keep the water cool in summer

The air stone first, then shade and burying the tank, a large light-coloured container, ice blocks for hot days and a water chiller for large setups. For winter, a heater and insulation come in.

Water chiller

Ideal for warm climates or high temperatures to actively cool the water.

If you have a large setup with many plants, or the water keeps rising above 25 °C in summer despite shade, a water chiller from the aquarium trade helps. It keeps the temperature constant, and you no longer have to worry about it. For a single tower, shade, burying the container and an air stone are usually enough. If you have a solar system and plenty of spare electricity in summer, a chiller is a nice solution.

Aquarium water chiller for large containers

A water chiller is mainly worthwhile for large hydroponic setups. In a system with 20 to 120 plants there are already many different values and parameters to consider. You do not want to have to worry about water temperatures that are too high as well, which increase the risk of root rot and in the worst case could destroy the whole harvest. A water chiller helps keep the water temperature constantly at an optimal level. That is especially important to ensure plant health and prevent disease. With a water chiller you make sure your plants grow in an ideal environment without you constantly having to monitor the temperature.

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Aquarium chiller up to 160 litres

Completely over the top, but brilliant. If you have a solar system and do not know what to do with the surplus electricity, because feeding it into the grid makes no financial sense and the battery is always full in summer, this would certainly be my first choice. Keeps large containers constantly cool in summer.

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Water heater

Important in colder regions or in winter to warm the water to a suitable temperature.

I use an aquarium heater with a thermostat for this. It keeps the water at 18 to 20 °C and switches itself off when the temperature is reached.

Aquarium heater 50 W, adjustable

For spring, winter or the greenhouse. Keeps your water constantly warm, ideally in a well-insulated container.

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Insulation

Protect the water tank and the system with insulating materials such as polystyrene or insulating film to minimise temperature fluctuations.

With the Kratky method a polystyrene box keeps the temperature nicely stable, in spring as well as in summer.

Polystyrene box 46 litres with lid

This box can also serve as a water container. If you put in a liner, that is no problem at all and your temperature stays constant. My Kratky system with polystyrene works brilliantly. Keeps the temperature in the container stable, in spring as well as in summer.

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Food-safe liners for polystyrene boxes

These food-safe liners serve as a waterproof insert for your polystyrene boxes. They are ideal for early growing in spring and late autumn when temperatures are too cold, or for high summer when it gets too hot. The liners are waterproof and food-safe, so they are safe to use for your plants. While the polystyrene boxes help keep the temperature constant, the liners keep the system watertight. Perfect for Kratky systems as well as fixed systems such as NFT or screwed hydro towers.

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Circulation pumps

Constant water circulation helps balance the temperature throughout the system and prevents hot spots or cold areas.

Solar water pump for the nutrient container

This clever idea of mine helps you keep your nutrient container moving. Water circulation is important in hydroponics, and the solar-powered version needs no socket. On its own it does not help against algae; for that the container has to stay dark. The moving water surface also brings oxygen into the water, which is perfect for your plants root growth. This solution makes sure your plants are well supplied and can grow healthily.

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Shade and direct sunlight

Use shade nets or position the system so it is protected from direct sunlight, especially outdoors.

In the sun the tank heats up. Bury the container and cover it with white stones, so only the tower sticks out. The soil keeps the temperature much more even than the air. Or stretch a shade net over it. I also like to use a shade net when young plants are first getting used to the sun outdoors.

Frank’s tip

I drilled a hole in the lid and planted a mint in it. It grew so big that it shaded the whole container. And big tomatoes shade their containers all by themselves.

Shade net 2 x 5 m, 60 %

I like to use shade nets, especially when acclimatising young plants outdoors. Maybe you have already seen posts about it on my social media channels. Lettuce should be shaded, as it cannot take too much sun on hot days. These nets offer ideal protection. On particularly hot days you can also stretch the net over the greenhouse roof to protect your plants from excessive heat. I have never needed it for my tomatoes; the big plants shade their containers themselves. Protects containers and young plants from full sun.

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Adding cool water

At high temperatures, occasionally adding cool water from the fridge or ice blocks from the freezer can help lower the water temperature and manage short-term peaks.

If the water still climbs towards 30 °C on hot days, ice blocks help. I freeze water in small boxes with lids and put the closed box in the container. That way the ice cools without diluting the nutrient solution. For me one block lasts about 5 hours and lowers the temperature by up to 5 °C depending on the size of the container. That helps with heat peaks; for every day it does not replace shade and oxygen.

Angebot

Storage boxes 5 litres with lid, 10 pieces

These boxes are ideal for using ice blocks from the freezer when temperatures rise and the water temperature quickly climbs to 30 degrees or more. That lowers the risk of root rot. They are particularly useful when shading is no longer enough and you have no water chiller. Since the water hardly cools down on warm nights, ice blocks offer a simple solution. A block in warmed water lasts about 5 hours and, depending on the size of the container, can lower the temperature by up to 5 degrees for me. I freeze ice blocks in them. The closed box goes into the container and cools without diluting the nutrient solution.

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Deep water tanks

Tanks placed lower offer a more stable temperature, because they are less prone to rapid temperature changes.

A lot of water warms up more slowly than a little water. In a large container the temperature fluctuates much less, and you have to top up less often. Outdoors I use large light-coloured containers of 37 and 60 litres and bury them by the greenhouse. Light colours absorb less heat from the sun than dark ones.

White 60 litre container with hinged lid

Maybe you have already seen the smaller 37 litre version on my social media channels. Outdoors by the greenhouse I bury these 60 litre containers. The larger capacity is ideal, as I have to worry less about topping up the water. These containers have a handy flap that gives quick access while protecting against dirt. They are also white, so they absorb little heat from the sun and are perfect for burying.

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By combining these methods you can ensure a stable water temperature in your hydroponic system, which is essential for the growth and health of your plants. Regular checking and adjustment to the needs of your specific system are the key to long-term success.

☀️Great heat

My checklist for great heat

In summer a few minutes a day are enough. Every day I check the water level and water temperature, whether the pump and air stone are running, and look at the leaves. When it gets really hot, I go through this list:

In great heat

Set the pump to 15 minutes on, 15 minutes off. Normally mine runs 5 minutes on and 30 minutes off.
Top up water more often, container in the shade.
Let the air stone run continuously, straight from the socket.
Cooler again? Back to 5 minutes on, 30 off.

At an air temperature of 35 to 38 °C growth stops, and tomatoes already set less fruit from about 30 °C. That is why my greenhouse is completely open in summer and the side panels come out. A through-draught is the best thing against heat and humidity.

📏Measuring

Measure instead of guess

A thermometer in the container shows you immediately whether you need to act. Many pH and EC meters also measure the temperature. That way you have all three values that belong together at once. In summer I look at the water level and water temperature every day; it only takes a moment.

My recommendation for getting started

5-in-1 meter for pH, EC, TDS and temperature

Affordable, easy to use and perfectly adequate for beginners.

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When	What I check
every day in summer	water level and water temperature, are pump and air stone running?
every few days	EC and pH, always EC first, then pH
at night in spring	does the water cool below 18 °C? Then I wait before moving outdoors
with problems	always all three: EC, pH and water temperature

Do not change the nutrient solution by the calendar

Even in warm weather I do not change the nutrient solution by the calendar. I measure every 2 to 3 days, EC first, then pH, and top up with ready-mixed nutrient solution. It only has to come out completely when the EC rises for no reason or deficiencies appear even though pH and water temperature are right.

Water without fertiliser	EC in mS/cm
soft	below 0.3
medium	0.3 to 0.5
hard	above 0.5
Rainwater or reverse osmosis water	almost 0

How often the pump needs to run in heat, you can read in my article How often does the water run in hydroponics?. In the NFT system the nutrient solution lies as a thin film in the channels and reacts particularly quickly to sun; more on this under the Nutrient Film Technique. With the Kratky method a polystyrene box keeps the temperature nicely stable.

Frequently asked questions about water temperature in hydroponics

What water temperature is ideal in hydroponics?

Between 18 and 22 °C. In this range the roots work well, nutrient uptake runs steadily and the water still holds enough oxygen.

Up to what water temperature is it still fine?

Up to 24 °C it is still fine. From 25 °C the water is too warm, and then you have to take action.

From what temperature is the water too cold?

Below 18 °C. Then the roots work more slowly, and the plant takes up fewer nutrients and grows slowly, even if EC and pH are right.

From what temperature is the water too warm?

From 25 °C. Warm water holds less oxygen, stress for the roots increases, and root rot can develop faster.

Why does warm water hold less oxygen?

The warmer the water, the less gas can dissolve in it. At 20 °C about 9 mg of oxygen fit into a litre, at 30 °C only about 7.6 mg. At the same time the roots breathe harder in warmth and need more of it.

What helps first with water that is too warm?

An air stone, shade and a sheltered spot for the tank. Outdoors from a water temperature of 25 °C the air stone is a must.

Why do EC, pH and water temperature belong together?

All three decide whether the plant can take up its nutrients. If a plant has problems, always check all three.

Why do leaves sometimes become mottled in spring?

That is often due to the water temperature. At night the nutrient solution is then often only 11 to 12 °C, and the roots do not take up all nutrients. So do not add more fertiliser. As soon as it gets warmer, everything recovers.

What do dark, purple-tinged leaves show with cold water?

They show phosphorus deficiency. It often occurs with cold water, because the roots then take up less phosphorus, even though there is enough in the nutrient solution.

Do I add more fertiliser if the water is cold?

No. The fertiliser is there; the roots just take it up more slowly in the cold. More fertiliser does not help. Better keep the water warmer.

How do I keep the water warm in winter?

With an aquarium heater. I use it to keep the water constantly at 18 to 20 °C in winter. A well-insulated container, for example wrapped in polystyrene, holds the warmth longer.

When does the tower go outdoors?

I only move the tower outdoors from mid-May. The water should be between 18 and 22 °C, roughly room temperature, and before that it cools down too much at night.

How do I protect the water tank from the sun?

Bury the container and cover it with white stones so only the tower sticks out. Or stretch a shade net over it. A large, light-coloured container also heats up more slowly.

Why does a small container heat up faster?

A little water takes on heat quickly and gives it off quickly. In a large container the temperature fluctuates much less. That is why outdoors I use large containers and bury them.

Can I put ice in the water?

Short-term yes, ideally as an ice block in a closed box, then you do not dilute the nutrient solution. For me one block lasts about 5 hours and lowers the temperature by up to 5 °C depending on the container. Long-term, shade, a large container and oxygen help.

When is a water chiller worthwhile?

For large setups with many plants or if the water keeps rising above 25 °C in summer despite shade. For a single tower, shade, burying the container and an air stone are usually enough.

Why does root rot develop faster with warm water?

Warm water holds less oxygen, and pathogens such as Pythium like it warm and low in oxygen. Root rot is usually caused by water above 24 °C, light or dirt in the container, or too much fertiliser.

How do I recognise root rot?

Healthy roots are white and strong. Rotten roots are brown, slimy and smell musty.

What do I do about root rot?

Cut off the brown roots, clean the container, mix fresh nutrient solution and let the air stone run. Also provide plenty of air movement.

Do more algae grow with warm water?

Algae mainly need light. I have no problems with algae even above 30 °C, because my container is closed and hardly any light gets in. On top of that the air stone always runs in warm weather.

Does the air stone only run during the day?

No. Roots breathe day and night. That is why the air stone does not go on the timer but straight into the socket and runs continuously.

What do I measure the water temperature with?

With a thermometer in the container. Many pH and EC meters also measure the temperature, then you have all three values at once.

How often do I check the water temperature in summer?

Every day, together with the water level. In the sun the tank heats up quickly. It only takes a moment and shows you immediately whether you need to act.

What water temperature do tomatoes need in the tomato tower?

For tomatoes I keep the water at 18 to 24 °C. The air stone always runs in the tomato tower, and each container has its own.

Can I add hydrogen peroxide to the nutrient solution against algae?

No, not with the plants. Even small amounts can damage the roots; in a study, lettuce with mineral fertiliser grew poorly with it. I only use 3 % hydrogen peroxide for cleaning the empty system and rinse thoroughly afterwards. Against algae, above all a dark, closed container helps.

Do I need an air stone in the hydro tower indoors?

It can run but does not have to, because the trickling water picks up air. Outdoors from a water temperature of 25 °C it is a must. In the propagation station and with DWC, where the roots stand in water, it always runs.

How long does the pump run in great heat?

Normally mine runs 5 minutes on and 30 minutes off. In great heat I set it to 15 minutes on and 15 off. When it gets cooler again, I go back to 5 on and 30 off.

Does a circulation pump help against algae?

No. Movement in the water does not stop algae; they need light. But a circulation pump evens out the temperature in the container and brings oxygen into the water via the moving surface.

Do I have to change the nutrient solution more often in warm weather?

Not by the calendar. Every 2 to 3 days I measure EC first, then pH, and top up with ready-mixed nutrient solution. I only change it completely when the EC rises for no reason or deficiencies appear even though pH and water temperature are right.

Is my tap water soft or hard?

Measure it without fertiliser: below 0.3 mS/cm is soft, 0.3 to 0.5 medium and above 0.5 hard. Rainwater and reverse osmosis water are almost at 0.

You will find more basics in my guide to hydroponics, on Types of water, on EC value and the pH value.

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