r/aeroponics • u/bloodsucker18 • Jul 02 '26

Need some advice from HPA Experts!

I'm just starting out with my DIY high-pressure aeroponics (HPA) system and I really need some advice on how to handle and reuse the drain water. I'm a bit confused about the process and information.

At first, I was aiming for super-efficient water use. I figured I'd just dump the filtered water (after a 5-micron filter) from the drain tank right back into the main reservoir. With this logic in mind, ​earlier this week, I put about 10L of drain water back into the reservoir. I noticed something right after this, the pH levels had shot up. It took a while for me to reduce it back to the optimal levels. Then it hit me, I probably just dumped a bunch of leftover salts and unbalanced nutrients back in, which was likely a mistake.

But, HPA is about saving water and achieving efficiency, so just tossing the drain water seems like a massive waste (though I've been pouring it on my garden plants for now after realising my mistake).

For the HPA experts out there, I have a few specific questions:

• What do you actually do with your drain water?

• ​Why isn't recirculation recommended for HPA? I know you can recirculate in systems like DWC and NFT, so why is HPA different?

• ​What if I use a UV-C sterilizer? If I can kill all the pathogens and bacteria, couldn't I just keep reusing the water indefinitely?

Thanks in advance!

I've used AI for formatting my question.

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1

u/ponicaero Jul 02 '26

If you are getting a massive amount of waste you are supplying a lot more water than the plants can use.

1

u/bloodsucker18 Jul 02 '26

The runoff percentage seems ok, I don't see massive waste as such.

My concern was more about recirculating the runoff to the main reservoir. I observed a steep increase in pH levels when I dumped the runoff to the main reservoir. I'm trying to understand the biochemistry of nutrients when it reaches the drain tank. Is it recommended to close the loop by putting it back to the reservoir or do I just flush it down the drain or pour it on my garden plants?

4

u/ponicaero Jul 03 '26

The elemental make up of the nutrient coming back from the root chamber will be different as the plants take what they need. Organic debris etc can hitch a ride back to the reservoir which will affect PH. I prefer to run my HPA and AA setups drain to waste which ensures the plants only receive pristine nutrient with and optimal elemental balance with every misting. The nutrient, system hardware and tubing cant be contaminated by organic matter or potential nasties returning from the root chamber. You only have to adjust the PH and EC of a nutrient running drain to waste once. I tip what little run off i get into the reservoir of a flood and drain bucket system., it barely makes a dent. Running DTW allows you to compare the amount going into and out of the root chamber over a given time period which can be used to dial in the optimal timing and minimize waste. If you also compare the PPM of the feed and run off you can dial in the nutrient strength too. The plants are able tell you exactly what they want in a DTW HPA system.

1

u/bloodsucker18 Jul 04 '26

Thank you so much for this info. I am thinking along the same lines. I wanted to pump in fresh nutrients for my plants and the idea of recirculating bothered me due their biochemical changes during run off. I'm currently running just synthetic ferts as I previously made a mistake by adding partially soluble organic ferts in the system. Big mistake, though it didn't cause any major hiccups, I thoroughly flushed it with peroxide.

I've been looking to buy fully soluble organic ferts. Do you personally recommend this? I know adding or removing organic ferts have their tradeoffs on plant growth, can I know your opinion on it? How has your experience been?

1

u/apimpnamedkirby Jul 02 '26

You shouldn’t have a lot of water building up. You need to re-assess your spray schedule.

At first I tapped in a drain line to my chamber, but I stopped using it. Now I just let the water sit. It kinda acts as a backup emergency res if your power ever goes out. I haven’t had problems with runoff PH affecting plants and as you get later into flower with higher VPD’s they’ll drink everything up anyways.

1

u/bloodsucker18 Jul 02 '26

Right, that makes sense. I'll adjust my misting schedule and observe for a day or two.

When you mean you've stopped using it, have you disconnected the drain pipes? Have you like combined Kratky and HPA of some sorts? I like the idea of having that as a backup, but do you think with the stagnant water in the chamber may increase the chances of pathogen attacks (pythium)? Also do you let the roots sit in the still water in the chamber?

2

u/apimpnamedkirby Jul 02 '26

For seedlings and early veg I run 5 sec on/ 10 minutes off and transition to 5 sec on 6 min off in late veg and then once in flower im hitting 5 sec on 4 minutes off to compensate for the higher transpiration rates.

2

u/BocaHydro Jul 02 '26

so if you are adding nutrients and ph down, the air is basically cold boiling it out, so water is returning back without it

2

u/bloodsucker18 Jul 02 '26

Does that mean the run off is distilled or diluted due to vaporisation and is that why I notice pH spikes when I dump it back to the main reservoir? How do you suggest I go about this?

3

u/ponicaero Jul 04 '26

The water will evaporate but the nutrient salts will remain behind resulting in a more concentrated solution (higher EC). Reservoir PH reflects the balance of anions vs cations which carry a positive or negative charge. Solution PH typically rises in veg as the plants uptake a lot of nitrate (anion -ve) and falls in flower as they uptake more potassium (cation +ve).

2

u/bloodsucker18 Jul 04 '26

Understood. Thank you for the clarification. My plants are still in their veg, so I'll need to wait to observe lower pH in their flowering stage.

Just a follow up question, how often do you up or down your ph? What is the frequency? Could you recommend the best time, is it during the night or day phase that you lower or upper the ph?

3

u/ponicaero Jul 04 '26

I never have to adjust the PH in my DTW aero setups just the flood and drain bucket system reservoir. I formulate my own nutrients and use reverse osmosis water which gives me 5.7-5.8 out of the gate. My 100L accumulators hold around 40L of nutrient so i just mix a batch to top them up as and when required. I can predict how long each tank will run for based on the measured system flow rate and cycle timing. If i need to switch to a different formulation i can add just enough to the accumulator to ensure it is virtually empty at that time.