Backyard Aquaponics
A place to discuss aquaponics

The calcs on the system are good so are results. But is there a formula for airation which could be harmful to the fish? Seems like a silly question but I would like to add more airation to the plants but don't know the answer to this probably simple question for you all.

IMHO there is no maximum DO (Dissolved Oxygen) that will harm fish. DO will not increase above the percentage dictated by the water temperature (The colder the water , the more DO)
The only way that DO will disturb the fish is the manner and amount of physical water disturbance you use to produce the DO.
I'll probably be kicked in the teeth again for offering this piece of profound wisdom , but I don't care!!

Cheers Ian K

No teeth kicking required Ian... you are correct...

You can't really have too much aeration... and unless you're using pure oxygen injection, there's a limit to how much oxygen can be dissolved by the use of normal air aeration...

This relates to the fact that normal air contains 21% oxygen, the remainder being essentially nitrogen.... this can be a problem in terms of the overall nitrogen load, along with the normal feed, ammonia production.... and rewuire extra filtration...

It is possible to super-saturate using pure oxygen, and this can be dangerous, particularly if the injection is by very fine bubbles....

The point you raise about disturbance to the fish by massive injection of aeration is valid...

If you aerate too violently.. you can force dangerous levels of suspended particles through the fish gills... obviously good filtration will alleviate this problem...

But also high levels of aeration leading to bouyancy and flow issues can also be problematical.... as they lead to the fish stock expending vast amounts of energy to counter the effects of bouyancy or flow.... leading to slow or poor growth rates... as they expend so much energy doing so...

Thanks. I am not too worried about disturbing the fish. I have two manifolds with three returns each. They all enter the resivior about 1/2" above the surface level and are all contained on one side of the resivior covering about 2x14 inches. I actually put another small pump in there just to circulate the water a little which the fish seem to enjoy. Thanks again.

Oxygen is only dangerous at considerable pressure O2 at 1.6atm or air at about 9 atm will be dangerous, but for our purposes, nah, can't hurt em I wouldn't think.

Ian how could they kick teeth surrounded by a colorful beard, everyone is bound to have different opinions, that's what the forum is about, for what it's worth I reckon Autocad is great but was staying outta that arguement, if I won lotto was going to get you to design my house on the river down south, but will have to wait for the next one

Hi Nocky,

I don't want to hijack this thread, but maybe I should have stayed out of it too!!!
The nominal aeration for my fish tank will be provided by means of a by-pass valve on the pumped outlet going to the grow beds when operating on 240V. On the occassion of Blackout, it will be provided by a 500GPH 12 volt submersible connected to a 'PowerStream' venturi. Automatic relay switch over and trickle charged battery.
Aeration also supplied via falling water returning to the fish tank from 90mm return stack, 3m above fish tank. Gets a fair turbulence down the stack and at exit.

Cheers IanK

I can only think of two probable ways that an APer might manage to super saturate (super saturation can be dangerous to fish because the micro bubbles can get into the blood and it would be like a human getting the bends while surfacing from a dive),
One would be if you use pure O2 for aeration under pressure. I will hope anyone using pure O2 will do their homework and not waste the extra money only to kill their fish.
Two would be a pump that is managing to suck air in with the water and by virtue of the pressure in the pump and plumbing just past the pump some how produces micro-air bubbles. If your pump is managing to suck in air with the water intake, then there is a leak that should probably be fixed as the whole situation could be hard on the pump. I don't think this situation is immediately dangerous to the fish unless that pumped water with the micro bubbles is being injected into the lower part of the fish tank. If the water is splashing into the top of the fish tank, there is probably time for the micro bubbles to escape before they could affect the fish. If the water is going from the pump to a grow bed, there is even less chance for the fish to absorb the micro bubbles

I agree if you pull a fish up too quickly from over 10 metres, they'll get into trouble, but I doubt no matter how you saturate the water that you could cause bubbles to form. we're talking of a pressure change less than 10% in most cases...

Yup, you're right TCL... and in the case of air entering the pump line... it's quite possible you could cause cavitation and kill your pump before you kill your fish...