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Re: Antisiphon holes in Filter return lines -- or How low can you go?

Rick Engstrom asked:

> would you not want that small hole below the water line ?

Hey, good point, Rick!

For the record, there's a couple of ways to approach this. 
If the hole is above the water line and your pump stops,
you won't siphon more water than what's in the hose up to
the point where the hole is drilled.  When the pump is
running, this hole will spout, cause some minor turbulence,
and help to throw off some CO2 -- how much CO2?  Depends on
whether the tank is covered, how much turbulence is caused,
etc.  I've never done a meausrement but I suspect the CO2
loss is relatively low, all things considered.  Also, it
will create some water noise.  You can put a piece of
coarse foam around the tube and that will minimize the
turbulence, noise, and probalby the CO2 loss.

If you put the hole below the water surface and the pump
stops, you'll siphon the water out of the tank until the
tank water level gets below the hole.  If you sump can hold
that much water -- no problem, no spill, no noise, no CO2
loss :-)  With a sump system, the sump "carries" the
changes in water level, when everything is working, and the
aquarium water level stays pretty darn constant -- so you
can put the hole very close to, but below, the surface and
not worry about the aquarium water level dropping down
below it due to evaporation when everything is working.

Scott H.

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