Contributed by: snoofer
Thanks to: burnaby, smoking fl, 430scrog, Bayou
grower, Mia Stoner, Seeker4TAO, Stoner133
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?
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.
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.
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.
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.
changes in temperature may shock roots.
- Frozen pop bottles/milk jugs.
Fill to . 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
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
- 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
amounts of cool intake air directly into the root
- 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
- 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
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.
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
Note: Cooling coils may not be useful for
those on metered water.
DIY heat exchangers: try
hot tub suppliers, home brew stores.