Maintaining a highly aerated root zone at optimum temperature is key to achieving high yields and problem-free grows. This FAQ focuses on indoor hydroponic reservoir cooling options.

Why do I need cool root temperatures?

High root zone temperatures often plague indoor growers running water culture (aero/bubbler/dwc/hydro) systems. These systems are subject to rapid heating by intense HID lighting, which increases root zone temperatures, which decreases dissolved oxygen (DO) levels. Rapid plant growth, combined with low DO levels, can cause oxygen deprivation which in turn can result in infection by opportunistic pathogens such as pythium.

The key to maximum growth is to keep the air temperature at 75-80F, but the root zone at 68F or less. Note: the reservoir should be kept slightly cooler than the rootzone - irrigation and system heating will warm the water by the time it reaches the roots.

Optimum root growth occurs at 70-75F; however, destructive root diseases also grow and reproduce rapidly at these root temperatures. Maintaining nutrient temperatures at or under 68F maximizes root growth and DO, and inhibits pythium.

Reservoir cooling options:

Warm summer temps often require aggressive cooling measures. Bubblers and dwc are difficult systems to temperature regulate due to their (usually) small volumes and lack of external reservoir.

Note: spray / drip / mist / circulate nutrients on a frequent basis to equalize reservoir and root zone temperatures. Intermittent spraying may require a slightly lower tank temp, to compensate for system heating occurring during "off" spray cycle. (ie. Keep tank temp around 64F for intermittent spray cycles, 68F for continuous spraying).

Note: submersible pumps add heat. Use an external/inline pump to minimize heat transfer. High quality digital thermometers are recommended.

• Add cold water when topping up.
  Note: abrupt changes in temperature may shock roots.
• Frozen pop bottles/milk jugs.
  Fill to ¾. Keep extras in the freezer to replace thawed bottles with new frozen ones, replace as necessary. Note: "Freezy packs" tend to crack and leak.
• Increase size of reservoir
  Larger volumes are slower to warm up, pH/ppm is more stable and tank changes are less frequent.
• Put reservoir/bubbling buckets onto floor, or set on concrete blocks to conduct heat away from the water.
• Insulate
  Paint all exposed system surfaces white or use reflective material (such as mylar or reflectix). Wrap insulation around tank. Use a camping cooler for a reservoir (pre-insulated and comes with a drain!).
• Swamp cooler
  Blow a fan directly across the surface of reservoir for excellent evaporative cooling. This method works well (expect a 10F drop in res. temp), but humidity and tds will increase, and more frequent topping up will be required.
  
  430 scrog "?add a computer fan to a duct blowing into your tank (cut air exit holes). You can run it on a timer (1 hr on, 1 hr off). I run a float valve to keep it topped up."
  Make sure lid and reservoir can be easily removed.
• Blow air through the root zone
  Divert small amounts of cool intake air directly into the root zone.
• Remote reservoir
  In-room reservoirs will quickly heat up to room temp. Put the reservoir (and ballasts) outside of the grow room to minimize tank heating.
• Airstone / Power head / Venturi air supply should be drawn from a cool source (ie. Cool outside air).
• Peltier coil (Thermoelectric chillers).
  (Bayou grower) "I use an Ice Probe ($125) and it works well. It uses 50 watts and pulls the temp down 4 degrees under ambient. Cools 10 gal or less." (see coolworksinc.com for more models)
• Reservoir chillers
  These are electric A/C units made specifically for cooling water. (Search for "Aquarium chillers")
  (smokin fl) "?a heavy box with fan and compressor coils, with a 5 foot refrigeration line with a titanium coil at the end. All you do is plug it in, set the controller and put the coil in the res. Circulate nutes for the best cooling. Get a bigger model than you need."
• Cooling coil

A coil of stainless steel is put into the reservoir, cold tap water is trickled through the coil and the overflow runs down the drain. A circulation pump in thte rez makes the cooling more efficient. Adjust tap flow as necessary (Water use can reasonable). No power, unlimited cooling, quiet.

Making your own cooling coil:

Scrap yards and appliance repair shops are full of A/C and fridge coils: 4-20 loops (more surface area is better), with male garden hose connectors welded to each end (Don't use copper or nickel coils). Available in Hydro stores (around $100 cdn).

Note: Cooling coils may not be useful for those on metered water.

DIY heat exchangers: try hot tub suppliers, home brew stores.

awesome thread! i have a built in resevoir under my table. what is the best way to chill the res? should i just put frozen water bottles on the table and let the bottles cool the water while having a fan blow on top of the table? my current water temp is 77 degrees and i am a little worried. will this shock the roots? thanks!

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Everything I say on this forum is truth. All pics I post are mine and not from the internet.

How cool is too cool???

Say... water at 58F to 62F... root zone at 66F to 68F.... plants at 70F to 72F...

Is it just slowing growth? or are there other detriments?

Thanks!

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Good aquarium chillers are $400+ ... there is a better solution.


Craigslist Go on craigslist, find a water cooler... you know the ones you put jugs in, push the button, and you get water to drink ....

I see them for under $30 all the time. Rip it apart, and make use of the coils =)

i have been pulling my hair out trying to find a good way to diy a cooling unit
i think i have finally found a cheap way to do it. i will test it out and let ya all know what i come up with
Stay tuned!

Let us know how it turns out!

Anyone using a ebb & flow system have any problems with water temp rising?

What about converting a PC water cooling kit? I have already used PC fans that I pulled off these mini radiators that the water passes through and get cooled by the radiator and the fan attached to the radiator. Its all a 12 volt DC system and very easy to convert both the fan and water pump which could be mounted right on the side of the outside of the tank....a couple of 12v DC adapters for power to fan and pump and your all set.

It should circulated the water from inside the tank through the cooling resevoir and bump back in cold water into the tank.

Just thinking aloud here...I just remember how easy it was to convert a 4 1/2 inch PC cooling fan mounted on the back of a PC cooling radiator for the PC cooling unit and splicing to power to 12v DC adapter I had layng around and then using that for a exhust fan. All else needed was a 10 foot piece of dryer hose to make the exhaust vent.

Well so far the plans are looking good. One can actually do this without drilling any holes in the tank which is no big deal for the tubing for the inlet side. The outlet side after water has been run through cooling radiator can also be layed over top with the power power to the submeged pump or you could drill another small hole at the top of the tank somewhere for your return water thats nice and chilly......

Only obstacle I ran into so far is matching up the tubing and fitting size. Seems I got 2 or 3 different type PC water cooling kits around and they all dont use the same size tubing. SO once I get some more cheap tubing I should be all set. This is all gonna be mounted externally either directly mounted on the outside of the tank, or a nearby shelf will work nicely also.

Ill ppost some pics after I get the tubing I need.

BTW- just in case any are interested, Im using parts prom a thermaltech and Bigwater PC water cooling kits. The fan on the radiator is 4.5 inch fan size...standard 12v DC.....I can give you more specs if you have specific questions.

Could someone explain in detail how you would go about running a fan to blow air across the water thats inside the tank? In one of these post that was suggested as a way to keep res temps down...just wondering exactly how that would work....


Thank You!