shrimp- and plankton-safe pumps

[eraserbones]

A few months ago my (presumed) Malayan shrimp produced a zillion larvae that spent a day or so drifting about the tank. I never got to find out whether or not they can survive in fresh water, though, because my filter did its job, and filtered them out.

This has me wondering... is there any way to keep the water in a tank circulating without filtering or killing suspended organisms? I would be tempted to just run a powerhead without any filter attached at all -- that'd probably work fine for microorganisms, but would no doubt chop inquisitive small fish and shrimp to bits. I've done a google search on 'plankton-safe pumps' and read a lot about abstract pump design, but never got an answer to what I might use in an actual, real-world tank.

The only real idea I have at this point is to go back to the basics and try an undergravel system. Perhaps spreading the suction over a large area will allow plankton to avoid being either chopped by the impeller or pinned against the filter medium. (Of course, if that's true, then that leaves me wondering why undergravel filters work as 'filters' at all. )
Other related questions:

- If you raise shrimp with a planktonic larval phase, what do you use to power your filter or circulate your water?

- Does anyone know of a plankton-safe pump (diaphragm, peristaltic, etc.) that's actually practical for aquarium use? All I can find are systems meant for pumping blood -- presumably very expensive and not really designed for continuous use.

[Bradimus]

Have you considered a simple sponge filter?

[TKD]

Or putting a sponge over the intake of your filter?

[eraserbones]

A sponge filter is more or less what I have now (the first stage of my filter is blocked by foam.) But, the thing is, it's a _filter_. Bits of stuff in the water column (phytoplankton, smallish organisms, larval shrimp) are strained out of the water, presumbly depositing in a small, dead layer on the surface of the sponge.

So, sucking water through a sponge seems like the opposite of what I want. Anthing that's floating ambiently in the water (that is to say, plankton) is going to get sucked into the sponge eventually.

Am I suffering from some failure of imagination, here? Maybe all the organisms that I'm thinking of are all active swimmers anyway, and aren't endangered by the suction?

[Mustafa]

When people say "sponge filter" they usually mean the types that are air driven. The flowrate through the sponge of those filters are so low that no larvae will ever get sucked in. In sponge filters lower flow rates are actually better than super high flow rates since the low flow rates provide for more contact time with the nitrifying (and maybe denitrifying?) bacteria in the sponge. Anyway...a *real* air driven sponge filter is what you need.

[BARNY]

So would this type of filter need to be cycled with either fished or fishless cycling before putting shrimp in the tank?

[eraserbones]

OK, it seems reasonable that an air-driven sponge filter wouldn't suck up too much (although I assume that it would eventually filter out phytoplankton since it does, eventually, pull some water through the sponge.)

I'm not sure that an air-driven filter will really solve the 'circulate the water' part of my problem. But it may be that I just need to get over it, and accept having still water in the tank.

Planted-tank guides are always emphasizing that I want lots of water circulation (several times the volume of the tank per hour) and that I shouldn't use aeration because that drives out the CO2. But that style of tank generally seeks to emulate a river, which probably doesn't have much suspended plankton anyway. If I stop thinking 'river' and start thinking 'marsh' everything starts to make more sense -- might be better for the shrimp anyway.

[sif]

So would this type of filter need to be cycled with either fished or fishless cycling before putting shrimp in the tank?

Yep

[Mustafa]

I'm not sure that an air-driven filter will really solve the 'circulate the water' part of my problem.

And air driven sponge filter will circulate the water to some degree actually...just slower than a powerhead. Yes, it will drive out any *additional* CO2 out of your planted tank, but adding CO2 to your tank is likely to cause PH fluctuations anyway which can kill your shrimp.

[Bradimus]

Planted-tank guides are always emphasizing that I want lots of water circulation (several times the volume of the tank per hour)

I wonder if this has ever been scientifically tested. It seems possible to me that these guides repeat the same accepted traditions without ever examining them.

and that I shouldn't use aeration because that drives out the CO2.

Surface agitation will definitely reduce CO2 levels. But, you need to ask yourself if this matters. In general, supplimenting CO2 is only necessary if (a) you want unnaturally quick growth rates or (b) you want to keep submerged plants that are not adapted to this lifestyle.

[fatboy]

Eraserbones, what about using an airpump without a filter attached? I don't know if bubbles would damage the livestock. Is this why it has not been suggested yet?