In Thai grow rooms without air conditioning, a hydroponic nutrient tank often sits at 31 °C instead of the usual 22 °C target. At that temperature, roots need more oxygen and the water holds about 15% less of it. Pythium root rot also spreads more easily.
Growers respond in three ways. They cool the solution with a chiller, add aeration and beneficial bacteria, or switch to coco or a drip system where the solution drains away after one use. This part compares the three options side by side. It checks where the popular yield figures for root cooling come from, lists what to measure in your own system and gives a recommendation by system size.
This is Part 2. Part 1: Running Hydroponics at 31 °C Reservoir Temperature: Chiller, Beneficials, or Change System
The three options side by side
A short reminder of the terms:
- Thermoelectric (Peltier) chiller: a cheap cooler without a compressor. It cools only a few degrees below room temperature.
- Compressor chiller: works like a small air conditioner and can hold water well below room temperature.
- Run-to-waste: each dose of solution passes through the pot once and is not reused.
| Cost | Removes the cause? | Works on a larger scale? | Main way it fails | |
|---|---|---|---|---|
| Chiller | Peltier ~USD 80 (≈2,500–3,000 THB); compressor ~8,000 THB and up | Yes, if correctly sized. Peltier units are weak in hot rooms | Poorly. It releases its heat into the room | Too small for the heat load; one breakdown stops cooling for the whole crop; condensation |
| Aeration + beneficial bacteria | Low | No. Limited by how much oxygen warm water can hold | Yes | Can’t raise oxygen above the 31 °C maximum; no data at tropical temperatures |
| Switch to coco or run-to-waste | Cost of the growing medium | Removes the problem | Yes | Loses the water and fertiliser savings of reusing solution, and some control |
What to do: write your own price quotes and your measured room temperature into a copy of this table before you choose. The table only tells you something once the numbers are yours.
Root-zone cooling: the yield figures and what is behind them
Two figures for cooling the root zone of cannabis get repeated widely. They are “25% more vegetative growth” and “often 40% more yield”. They appear in horticulture trade news sites such as HortiDaily and MMJDaily, and people quote them as if they were proven.
The forum’s editors traced both figures. Both come from equipment suppliers.
Root-zone temperature has been studied a lot in other crops, including lettuce, tomato, pepper (paprika) and cucumber. As of October 2026, the editors found no peer-reviewed trial on cannabis root-zone temperature that reports yield figures.
That doesn’t mean root-zone cooling fails. Warm roots respire faster, and warm water holds less oxygen. Together with the results from other crops, that makes cooling very plausible for cannabis too, and probably more useful in the tropics than anywhere else. The problem is narrower: no published cannabis trial supports the specific percentages people quote.
If you budget for a chiller because of “40% more yield”, you are budgeting on a seller’s claim. Cool the root zone because the biology is sound and because the cost of not cooling is Pythium root rot. A percentage printed in a trade magazine is not a good reason.
What to do: leave the 25% and 40% figures out when you work out whether a chiller will pay for itself. Base the decision on two things: the root-rot losses you have actually had and the temperature you have measured in your own solution.
What to measure in your own system
Tank temperature, recorded around the clock. Use a logging thermometer, which records the temperature by itself at regular intervals. The damaging reading is the daily maximum, and it usually comes several hours after the lights’ hottest period. A manual check at one time of day easily misses it.
Temperature where the roots sit, not only in the tank. Measure in the pots or channels as well. If the solution warms up on its way to the plants, the roots never get the temperature you paid the chiller for.
Dissolved oxygen, if you can borrow a meter. This is the oxygen the roots actually breathe, measured in mg/L. Almost no home or small commercial grower measures it. One week of oxygen readings next to your temperature record will tell you more about your system than any forum argument.
Root colour and smell, recorded every week. This is the cheapest early warning you have. The root-rot topic linked above shows what Pythium-infected roots look and smell like.
Your own electricity use for the chiller. This article gives no cost per gram for chilling. As of October 2026, the editors found no credible figure linking Thai electricity tariffs to grams of cannabis. If running cost will decide your choice of system, measure the chiller’s kWh over one full crop with a plug-in energy meter, then multiply by your tariff.
Translator’s note: Keep your temperature log running through the hottest months of your year. That is when the tank reaches its highest temperatures and the chiller works hardest. Readings taken in a cool month will make the chiller look stronger than it really is.
Recommendation by system size
Small volumes. Try the cheap fixes from Part 1 first: insulate and shade the tank, use more water, run the lights at night and use opaque tanks and lines. If that isn’t enough, add a chiller, and choose the right type. A cheap Peltier unit won’t hold 22 °C in a 35 °C room. Size the chiller by the heat load, expect to need a compressor unit unless the room itself is air-conditioned and test it before you rely on it.
Larger volumes. Work out the full cost of chilling. Include the chiller itself, the heat it releases into the room and the extra air conditioning needed to remove that heat. Compare that total with the cost of moving to coco. The editors expect this comparison to favour coco more often than advice from temperate countries would suggest. Choosing coco for this reason is a sound decision, not a sign of doing hydroponics badly.
In both cases, also run aeration with either beneficial bacteria or a sterile tank, but never both in the same tank. Part 1 explains the difference. This layer keeps the roots going when the chiller or the cooling fails.
Translator’s note: In Thailand, also plan for power cuts. A battery-backed air pump or a UPS (uninterruptible power supply) keeps oxygen going to the roots when the chiller and pumps stop. Any root product or oxidiser you add to the tank should be registered with the Department of Agriculture (กรมวิชาการเกษตร) and used as the label says. Ask the official distributor in Thailand for the registration number. The forum topic on what you may legally spray explains these rules.
Share your numbers below
Please post in this topic:
- the tank temperature you actually hold
- your chiller type (Peltier or compressor)
- your tank volume
If you have grown the same genetics in deep water culture and in coco in a Thai room, please post that comparison too. Right now, the question “is hydroponics worth it in Thailand?” rests mostly on opinions and on one overseas thread. Real numbers from local growers would help everyone choose a system.
Related reading on this forum: the hydroponic systems comparison in deep water culture, nutrient film and drip systems, plus the root rot, growing media and root zone topics linked above.
References
- Rollitup, “DWC Indoor in Tropical Environment”: DWC Indoor in Tropical Environment | Rollitup
- HortiDaily, “Cooling roots provides 25% vegetative growth increase in cannabis”: "Cooling roots provides 25% vegetative growth increase in cannabis"
- MMJDaily, “Root zone cooling technology provides often 40% more cannabis yield in high-tech greenhouse”: Root zone cooling technology provides often 40% more cannabis yield in high-tech greenhouse
- USGS, DOTABLES (dissolved oxygen solubility tables): https://www.usgs.gov/tools/dotables
- FAO, dissolved oxygen solubility in fresh water at 760 mm Hg (EIFAC 1986 values): https://www.fao.org/4/ac183e/ac183e04.htm
This article is technical growing information for education only. It is for readers who operate legally where they live, and it does not encourage cultivation where it is illegal. Every country regulates cannabis differently. In Thailand, cannabis flower is a controlled herb under the Notification of the Ministry of Public Health Re: Controlled Herbs (Cannabis), B.E. 2568. The Notification was issued under the Thai Traditional Medicine Protection Act B.E. 2542 and has been in force since 26 June 2025. Flower may be sold only against a PT 33 (ภ.ท.33) prescription from an authorised practitioner, covering at most 30 days. Advertising and online sale of flower are prohibited. Research, export, sale and processing of cannabis flower require a licence. The draft Cannabis Control Act is not law yet: the Cabinet approved the draft on 22 September 2026 and sent it to the House. Nothing here is legal advice.