Thanks TC and Ryan.
I've decided it's better for me to pay a little more up front and get the extended life from the linear piston air pumps (I can expect a good 5-7 years with these). Here is the AquaticEco page for them: https://www.aquaticeco.com/subcategories/3817/Medo-Linear-Piston-Ai...
The previous link I gave to the AquaticEco catalog is outdated, this one is current (see page 60 for the air pumps): http://mastercatalog.aquaticeco.com/
The linear piston pumps I'm interested in are made by Medo, here is a link to their nice new website detailing these air pumps: http://www.medo-water.com/index.html
For a handy chart showing backpressure PSI vs. water depth, go here: http://www.medo-water.com/koi_ponds.html
All of the tanks I'm using are Rubbermaid Stock Tanks, only 25" deep. That corresponds to a backpressure of ~0.86 psi.
According to the very helpful customer service guy at Medo, the Medo LA-45B is AquaEco's SL22, the LA-80BN is the SL44, and the LA-120 is the SL88 (by the way, I don't trust AquaEco's power measurement for the SL88, apparently they repeatedly measured 64 watts, as opposed to Medo's measurement of 111W. If correct, this would mean that the SL88 runs on less power than the SL44 (92W) while blowing FAR more air. Sounds too good to be true).
I was told that each of these pumps has an backpressure operating range which must be adhered to to ensure the long life. The SL22's is 0.71 - 2.13 psi, the SL44's is 1.42 - 2.84 psi and the SL88's is 1.42 - 3.56 psi, corresponding to airstone depths of 1' 8" - 5', 3' 4" - 6' 9", and 3' 4" - 8' 4".
This is important! For example, while the SL88 could easily provide all the air I need for my system, since my air stones will always be at ~2' depth I would end up running the pump way below its acceptable operating range, letting the piston run much faster than it should and causing premature wear. They do sell replacement kits that consist of pistons, gaskets and filters, but you should normally only need to replace the piston after 4-5 years as preventative maintenance. In my case then, I would need to modify the backpressure of the SL88 to get it into it's acceptable operating range, in effect wasting power on the throttling. Only the SL22 looks appropriate (without any pressure modification) for the depths I'll be working with. Good to know!
TC, when you give values like 1 cfm for the FT, is this always assumed to be normalized at 2 psi? Or do you mean I just need to get 1 cfm into my tank, whatever depth I put the airstones.
If the latter, then I think two of the SL22's would cut it for me (assuming 0.86 psi; here is the pump curve again): https://www.aquaticeco.com/images/static/pump-curves/SL22.gif
I would have to spend ~$40 more for two small pumps, but then I won't be using as much power (I won't get quite as much air as from the SL88, but I think it should still be fine, especially with a strong constant water flow/splashing in the FT).
It looks like Ryan suggests ~2 cfm at 2' though.. I assume this somehow accounts for 90 lbs of fish in a 300 gal tank? Is there a formula for this, or Ryan could you explain where the numbers came from? Thanks for providing them.
Finally, how effective is the splashing from a good inflow at suppling O2? I'm not sure how many CFM I should expect from this effect in my system. 0.5? 1?
TC, I think those AZOO backup pumps are ~$70. I'm not sure they're worth it for me.. I will post more thoughts on backup in a more appropriate discussion.
Thanks again, this community is so helpful!
the number I threw out was a very rough rule of thumb some one gave me a couple years ago when I was trying to figure out the backup air requirements for my system. He said you want 1 cfm of air per 400 gallons of fish tank and a rough figure of 1 psi to get air through an air stone and another psi to push air down below each 28" of water depth. Then if you want to get really in depth you start using the figures Ryan shared and you need to then look at the actual ratings of the different air diffusers and the fish load and temperature. I'm definitely not the expert in air pumps and oxygenation, all I got are some rough down and dirty rules of thumb to get started with. If you got fish/air pump/air stone experts to help you out, their numbers trump mine.
Water splashing is good for aeration. I like to have way more than enough though as redundancy rather than risk being low. It is amazing how fast fish can go belly up in hot weather due to lack of oxygen when something like a tripped pump circuit happens. Be sure the pump is on a separate circuit from the air.
Aha, an extra 1 psi to push the air through the stones.. for some reason I thought that was included. Oops. That sounds like a lot though. But if that's correct, I don't know if two of the SL22s will cut it for me after all. Unless I have a ton of splashing going on? I should have plenty there..
I was planning on running one line out to a surge protector that would be for my timer, two pumps (150W) and two blowers (100W). From your comment 'Be sure the pump is on a separate circuit from the air', I take it this is a bad idea? One of my water pumps will run constantly, while the other will be on a timer. I think the timer has it's own circuit breaker. Still too risky?
I just know that people have lost a whole batch of fish when they had the entire system hooked to one circuit and the CGFI tripped or some on unplugged it. See you are not likely to notice that the power is out to your system until you go out to check on it if the power is still on to the whole house.
Now when my fish were small and it was cool out, I was able to go overnight without anything running. I had a pump die at about 6 in the evening and wasn't able to go get a replacement till the next morning but that was with fingerlings in the spring. I've also heard of some one with tilapia in a 600 gallon tank (Now I don't know exactly how many fish and he seemed to thing the water wasn't that warm because the system was in the shade and not warming up to get the fish to grow as fast as he wanted) but the air hose came off his air pump (some time after the morning feeding) and by the evening feeding the fish were dead.
Now in my big system when I originally set it up. I didn't have any air going. But I was running a BIG pump constantly. My 300 gallon tank hand a constant waterfall running in and out of it probably well over 1000 gallons per hour and the 600 gallon tank hand the water fall going into it plus all the grow beds drained into it. Then when I did at first set up the air pumps they were set to only turn on when the power failed.
It will be up to you how much risk you want to take. I would suggest that once you are cycled up or fish you cycle up fishless, you might not need that many fish.
After all that research on air blowers I think I'm going to start off without any, and if I do eventually need more air (not convinced I will, for a few reasons) I think I will instead just buy bigger pumps rather than add air blowers and everything that comes with them.
Since the oxygenation occurs primarily at the surface either way, I don't see much point in pumping air to the bottom of the tanks, so that it can float back up and pop at the surface. Kinda seems like a waste of power, when instead you could be seriously disturbing the surface with a water pump AND contributing to turnover.
Thank you Kobus for your great post on the O2 debate, I think you have saved me a LOT of time, $$$ and inefficiency.
TC, do you know if the GFCI tripping issues occur only when other switches are involved in a timer circuit (e.g. a float-switch valve, like you mentioned)? Do you think I should expect problems if I have two pumps on one circuit (going through a battery backup), both pumps connected to a GFCI outlet with one of those pumps first controlled by a timer? The timer I'm considering has its own (15 amp) resettable circuit breaker.. so would that shut off the timed pump before the GFCI further back shut down both pumps? The other, continuous pump feeds the FT, so I want to be sure that one keeps going.
Thanks for bringing this up, I'm glad I'm thinking about it now!
I'm not sure on the GFCI tripping issue. I had that one pump switch keep tripping the circuit in the garage but I can't be certain why. I have a different pump hooked to that same float switch now and it's been working fine for a year and a half. I make a point of putting that pump on a separate circuit but it hasn't been a problem since.
Any way you get enough aeration is fine and appropriate provided you get enough aeration where you need it.
Ok, thanks. Do you (or anyone else) have a timer running on a GFCI outlet? Is that a dangerous combination? I would think it's pretty standard (and so reliable).
I've got timers running on GFCI outlets. You just can't really run a timer before a GFCI extension cable. Like I once tried hooking up lights on a timer but I needed to plug in multiple lights and the timer had only one outlet, so I thought it would be a good idea to put the little GFCI 3 way thing after the timer, the timer kept killing the GFCI until it quit working at all.
Truth is the one float switch situation I hand killing a GFCI was probably actually the pump causing some fault since I haven't had a problem since I replaced the pump, the switch is still working.
This thread discusses the timer + GFCI combo: http://www.talkingreef.com/forums/misc/3170-timer-tripping-my-gfci....
I think these people are using cheap timers for the most part though, but this does sound like it can be an issue.
Therefore I think I will try going from the main power through the battery backup, then split to two separate 20 amp GFCI outlets. One will feed the timer (with a built-in 15 amp breaker) and a pump for F/D cycles of the GBs, and the other 20 amp GFCI will feed the continuous pump for the FT. That way the more likely shutoff from the timer setup shouldn't affect my FT pump (I hope.. unless the shutoff is felt by the other GFCI?)
Is this what you meant TC about using different circuits? For some reason I was thinking I had to run different lines from the house. So then I was wondering how to best deal with the backup system.