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.
Here is an example of what I'm talking about. The growth is directly over an airstone.
I get what you're saying about raising up the plants for air to flow in between the raft-like container and the water. It would be simple to rig something like this up; however,will this damage the root base or dry it out?
This is an example of what I see over the airstones on a regular basis. (You should see the dramatic difference after only 2-3 weeks)
confirms all my thinking:
aeration is the main deciding factor in aquaponics as fish, bacteria and plants need it to thrive in good health
I always had second thoughts about the raft system as it diminishes the much needed oxygen exchange area between air and water surface
some of you may know my struggle against bubble aeration and airlift pumps: in my eyes they are not efficient
slowly but surely I have developed a concept which might provide a total solution
I was tempted to post it here
and I will, in due time
but first (you might not like this) I am going to file a patent for it before anyone else does to protect the idea for us all
rest assured, I like you guys so much and have over the years learned so much from you all it will be free for all to use for non commercial purposes (donations will be welcome)
"I always had second thoughts about the raft system as it diminishes the much needed oxygen exchange area between air and water surface"
Since this topic started I've been doing some reading on this question of aeration and oxygenation for raft application. I'm thinking along the lines that we will be dealing more with aeration in this area. Since mean water depth is only around 12 inches and at the resulting low pressure, I believe that less oxygen will be transfered by way of the smaller surface area to water of bubbles compared to that of surface agitation or surface to air interface. Larger pore stones will create more surface agitation underneath the foam as compared to smaller pore stones as well.
I'm very interested and wait to learn about your efforts here.
bubble aeration only becomes efficient if injected at depths over 7 m (21 ft)
this for two reasons: pressure differential and contact time
so your conclusion is right: surface agitation is more efficient
that is largely inhibited by the floating rafts
pumping a gas (air) is by the fact that it can be compressed by definition less efficient than pumping water
so you will get more water movement with a water pump
on the condition that it is an efficient pump
alas most if not all small pumps we use are extremely poorly designed and perform accordingly
I have calculated them: you are lucky to find one with 3% efficiency
furthermore it is important to lift the bottom water upwards: that is the coldest water which is more depleted and can absorb more oxygen
and it contains the most solids, thus the most bacteria and these crave for oxygen
Thank you for great insight and depth in your statements.
Frank said "furthermore it is important to lift the bottom water upwards: that is the coldest water which is more depleted and can absorb more oxygen"
So true. I thought about this in my FT design by choosing a circular tank and placing pump at center with inflow to create water rotation. The idea being to suck the surface water down toward the bottom suction of the pump. The reverse in the raft bed with inflow at bottom at an angle creating rotation(even though not as efficient with a rectangular bed) and outflow at top forcing water from bottom to top.
Since I'm depending on water movement for most of my oxygen transfer in water, I think design has a large part to play as well.
very original idea if I have well understood
so you suck the upper water down?
I like inventive people who dare to radically invert things
Thanks but this is hardly inventive( igot the idea from discussion with Kobus) as I'm sure many AP's are probably designed in similar fashion, but premeditating design with knowledge of oxygen transfer in water in mind is an advantage for the operator, as opposed to a willy nilly approach, don't you think? The important thing is the basic understanding of the relationships between water, plants, and media, and with that information we can design more efficient.
A friends system, here on the Big Island, uses 3 runs of soaker hose down each trough to get fine streams of bubbles. When I was visiting a few weeks ago, a center soaker hose was not putting out bubbles in one trough. The growth of the plants was substancially larger on the outsides of the trough than in the middle. This growth pattern was consistent down the entire trough. The center of the trough was not growing as fast because it did not have the benefit of the bubbles.
I personally have shifted most of my aeration to my troughs. I now have just enough bubbles in my FT to keep the poop moving and that's all. The rest of the air goes to the roots. The fish get plenty of DO from the water returning from the troughs. Since doing that I have had better and faster growth. The plants seem to get fuller and heavier with the extra aeration to the roots.
I believe that the aeration provided to the roots will promote more micro-organisms, bacterial and fungal growth on the roots themselves, than roots without extra aeration. The extra micro-organisms, bacterial and fungal growth on the roots helps the roots take in more nutrients which makes the plants grow faster. I do not think agitation of roots causes more growth because in nature roots are usually growing in dirt where there is no chance of agitation.
as suggested, oxygen is the main factor in keeping fish, plants and bacteria alive
within (time) limits you can take away food for the fish, and nutrients, even water for the plants
take the oxygen away and everything dies
so don't mess with oxygen
fish and bacteria are the most competitive for the oxygen
bacteria thrive on fish excretion
turn that excretion into nitrites (lethal to fish) then nitrates (not lethal to fish)
so it is imperative to remove the solids and bacteria as quickly as possible
therefore I am in favor of a continuous primary circuit over a biofilter
which can be either a pure biofilter or a growbed on which you grow plants that love constantly moving water i.e. watercress
having a pump in the fish tank will mince and spread the solids (and the bacteria) all over the tank, thus complicating the removal of both solids and bacteria
so I would put the pump in a corner of the biofilter or growbed where it pumps only filtered water
have the fish tank overflow into the biofilter (not the other way round), so that constant height is ensured in the fish tank
constant flow will ensure oxygenation for the fish
constant flow will ensure constant removal of solids and bacteria
constant flow will ensure oxygenation of biofilter or growbed
a secondary intermittent circuit to the growbeds ensures the oxygenation of plant roots and the influx of nutrients to the plants