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Aside from keeping the DO optimal for fish and plants, has anyone placed direct aeration under the physical plants and compared growth with those without? In a little experiment, I noticed a visible, positive difference in growth speed. Would agitation be a factor, stimulating the roots?

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There is a little more to it then that :) To properly calculate air needs, you would want to know:
Water depth
Water Temp
Fish Species (Warm water, cold water, baitfish, etc)
Diffuser O2 transfer rate (O2 lbs/hr)
Max Fish Weight

From there it's pretty simple, just plugging the numbers into an equation.

For troughs, UVI uses 0.5cfm every 4ft down the length of there troughs (4' x 100') and at that flow rate, the water stays saturated near 80% Do. In my personal testings, that amount of aeration through the troughs provides exeptional growth rates. You can still achieve growth with a lower CFM but the lower the DO, the slower the growth rates. I have an old chart from a hydro magazine from years ago plotting DO% vs growth rate and it was amazing.

TCLynx- the PSI needed to push through an airstone is different depending on who makes them. A lot of the medium pore diffusers take about 10" of resistance to push through the stone(0.37PSI) but if you go with a fine pore you might see something closer to 1psi drop through the stone. :)
at .75 Cfm in a 25" deep tank, you can support roughly 43# of fish without any additional aeration (at temps around 80 deg F)
Yea, I know my numbers were a really rough throw it out there to get some air into a fish tank. (Many air diffusers are going to vary depending on how long they have been in since their last cleaning and the rate they clog will vary depending on the pH and mineral levels in the water that might clog them.)

I'm curious, I've seen many discussions about how air stones and air pumps are not very effective means of aeration. (In my deep fish tank it is still fairly effective since it actually does quite a lot to circulate the water around to keep the bottom from becoming depleted.) Raft tanks are shallow and the circulation and bringing bottom water to the surface isn't as effective for aeration since the raft doesn't give much water surface access to air. So the air bubbles from the air stones in a raft bed are really doing the work.

After seeing some of those pictures of the plants right over the air stones and my own experience with small DWC hydroponics and how the air definitely improves growth. I wonder if there are any other more efficient ways to aerate DWC beds. I like the idea of suspending the plants above the water to allow more surface to air contact but this doesn't necessarily work well for operations that need the rafts to float conveyor style to plant at one end and harvest at the other.

Any ideas?
Hmm, don't know. I think the most efficient way to aerate a body of water is going to be a compressor/diffuser system. The deeper the body of water, the longer the bubbles have to rise and the more oxygen that is transfered into the water column. The only way you get better O2 levels is by bubbling in bottled oxygen through a fine pore diffuser. In shallow ponds you can use a paddle wheel aerator which gives a GREAT SAE (better then diffusers b/c of the shallow depth) but you would have to do some rigging to incorporate something like that into an AP system.

In my experience, if you have adequate aeration throughout the trough, you wont see huge differences in growth rates between plants directly over a diffuser and say one on the side of the trough. There is certainly a small difference, but ive never experienced a huge difference like in the previous picture a few posts ago.
In reading all of the responses concerning air flow ,I personally need a more experience person to calibrate air pump size for me. My system is 4troughs 32*4


















































































In reading all the respones concerning air flow would someone caluate for me the size of pump I need to supply air to 1300 gal water garden coupled to a250 gal solid settling tank,4 troughs 32ft +4 ft +9 inches than a55gal barrel . Any educated estimate would be apprecited.Thanks Paul
"I like the idea of suspending the plants above the water to allow more surface to air contact"

TC I too was thinking about this method to increase aeration but i think we'll have to factor in a 33% longer trough as we lose nitrification surface area by this amount.Maybe the added oxygen will support larger colonies on reduced surface area so that we may not have to extend the trough any if at all. Some input from our rafters may shed some light on this?

TCLynx said:
Yea, I know my numbers were a really rough throw it out there to get some air into a fish tank. (Many air diffusers are going to vary depending on how long they have been in since their last cleaning and the rate they clog will vary depending on the pH and mineral levels in the water that might clog them.)

I'm curious, I've seen many discussions about how air stones and air pumps are not very effective means of aeration. (In my deep fish tank it is still fairly effective since it actually does quite a lot to circulate the water around to keep the bottom from becoming depleted.) Raft tanks are shallow and the circulation and bringing bottom water to the surface isn't as effective for aeration since the raft doesn't give much water surface access to air. So the air bubbles from the air stones in a raft bed are really doing the work.

After seeing some of those pictures of the plants right over the air stones and my own experience with small DWC hydroponics and how the air definitely improves growth. I wonder if there are any other more efficient ways to aerate DWC beds. I like the idea of suspending the plants above the water to allow more surface to air contact but this doesn't necessarily work well for operations that need the rafts to float conveyor style to plant at one end and harvest at the other.

Any ideas?
There is a point. One could simply use more bio-filter to make up for the loss of the bottoms of the rafts instead of needing to enlarge the plant space. My raft tank is simply an add on to a system that already has plenty of media to handle the bio load of the system so the raft space is simply more plant space for my system.
How many lb's of fish at max are you planning on Paul? Id say 16cfm for the troughs(0.5cfm every 4').
Also need to know the fish tank depth as well as type of fish and water temp.


Ryan said:
Also need to know the fish tank depth as well as type of fish and water temp.
Ryan, My watergarden is 2 ft deep 8ft long 11 ft wide. The fish.I going to use are Talipia.The troughs are 32 ft long 4ft.wide 9 inchs deep. I hoping to keep the water temp at 60 to 80 degrees.Thanks for the input. Paul.Oh, the amount of lbs of fish is 130.
You would need a minimum of 2.45cfm to support 130lbs @ 2' deep. Add that to your 16 cfm for the trough and you need roughly 18.5 cfm @ 34" depth. I calculated this using 10" back pressure through the diffuser (typical medium pore diffuser)

Paul Ellinghuysen said:


Ryan said:
Also need to know the fish tank depth as well as type of fish and water temp.

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