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Martin, Electrical Engineer
Category: Home Improvement
Satisfied Customers: 4955
Experience:  Design, construct, fix and grow stuff around and in the home.
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I am trying to grow tomatoes hydroponically and I keep having

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I am trying to grow tomatoes hydroponically and I keep having issues with not having enough oxygen in my water. I have been trying to use live bacterial cultures which I have found to be killed by bubbling air into my solutions. I can use other means of oxygenating my water that will spare my bacteria but WHAT IS THE OPTIMAL VALUE OF OXYGEN IN WATER FOR HYDROPONIC GROWING AND WHAT KIND OF SENSOR DO I NEED TO MONITOR IT?
Hello, welcome to Just Answer.

I am not sure of how you use bacteria in your setup, can you describe it a little more (there is tons of way to grow stuff in hydroponic ways). I guess you use the bacteria as some kind of bio-reactor?
Customer: replied 7 years ago.
Well the question i suppose is two fold...

Plants obviously can't sit in just water... they drown and die. One would have to bubble air to the plant or flood it with water.

1. What is the optimal level of oxygen for plants?

Considering that plants like oxygen but our beneficial bacteria do not (a product like Great White as seen here: we must find a happy medium of o2 infused into our water. I know that Van De Zwaan of House and Garden nutrients reccomended at one point that we should not use air-bubblers with his nutrients because it may effect the "beneficials". This is heresay to me but I digress.

2. What level of oxygen is great for plants but won't kill my darn bacteria?

1- Plant do not need oxygen, in fact they created the oxygen in the air we now have (it was done by cyanobacteria, a plant, million years ago). In fact there is plenty of plant that can live always in water (aquatic plant). What kill the plant, by making their root root, is bacteria. Especially those that are anaerobic (thrive without air). Some system use UV in the tube to kill the bacteria in the water to prevent rotting. Aquatic plant survive there with antibacterial agents and tannins.

The product you linked are mycorrhiza product (i know them well i worked for Premier Tech maker of Mycorize TM for a while). Those are not bacteria but fungi that live in symbiosis with some plant (not all of them). They act like a catalyst to fix the nitrogen of the air in the soil so that the plant can absorb it.

The idea of hydroponic is to only give the plant what it need at the right proportion. This mean it does not need anything other than the right minerals it can't get from air (it only take carbon from air in fact and use the hydrogen from water to make "hydro carbon" and then release in the air the oxygen "electrolyzed" from water). You can pretty much get good result with a bit of urea and some additional mineral (most you can get back by burning the plant at the end of it's life and use back the ashes.

2- Any bacteria in a closed system will eventually die if they lack food or are surrounded by too much byproduct, it's not always an oxygen problem.

The amount of oxygen for mycorrhiza can be really high as they usually naturally live close to the surface of the soil. To prevent root rot, you can immerse them, then remove water, in cycles. You can also spray water and you can, like you mentioned, pump air trough air stone to make the water flocculate. The most efficient way is to spray water but you need backup pump because the root can dry fast in a pump failure.
Customer: replied 7 years ago.
Here is my real problem, I use an ebb andflow system called the "ebb and grow". It as a system of buckets filled with hydroton that flood for 15 minutes and drain. My problem is that the buckets do not drain completely and I am left with an inch of stagnant disgusting water at the base of every bucket. The roots hang into this water and turn brown since it is neither oxygenated nor completely exchanged. I have thought about modifying the system to drain fully from the bottom of the bucket but this would take a lot of effort and driling to accomplish. The fix that I thought would work would be to add an air stone to the bottom of each bucket. This would oxygenate the two inches of stagnant water and in my theory allow it to have some good root grown and antibacterial action. Later I learn that too much oxygen is bad for the "beneficial" bacteria but now you're telling me that this is not the case. Can I bubble too much air into the bottom of my buckets or would this fix work? If not, should I find a way to make the buckets drain entirely? The system is the C.A.P. ebb and grow and while it is great in some areas, it is incomplete due to this water problem. I am having a tought time solving this one... what does the mycorrhiza do to help me anyhow?
Mycorrhiza help with nitrogen, and not with all plant (it work especially well with Leguminosae). If you follow a process that already give nitrate with urea powder or something similar, they might not be needed at all. In any case that organism colonize the root, so when not in water they are fully exposed to oxygen.

Indeed, having root staying in still water will rot. Yes bubbling would help to not have dead water and you will never get more oxygen than the water can absorb (water get completely oxygen saturated in spay hydroponic method). Perhaps you could isolate them from the bottom of the bucket with a fine nylon screen for better draining around the root. You can also use a UV lamp to sterilize the water in the draining buckets, but if you use the same tubing for injecting water in the bucket and removing it, it will not work optimally.
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Customer: replied 7 years ago.
Thank you!