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[Bloggins]

I'm afraid it's too late for me to drill a hole. I have a 70 gallon tank, 20 gallon sump, with an Aquaclear 901 powerhead for the sump return. I am just starting to setup my tank. I tried doing a few test runs, with NO overflow boxes, just tubing to, and tubing from the tank.

I found that the rate of return from the sump, was greater than to the sump (as the powerhead was beating gravity. Will the construction of an overflow box really equalize the transfer of water to and from the sump? or did I make a critical error in powerhead selection?
(the Aquaclear 902, is multifunction, sump pump is one of them)

I'm a bit disconcerted, and think that an overflow won't help, but if it will, are there any parameters i have to keep in mind (ie Sump Box volume etc.)

Also a pet store dealer convinced me that I should buy substrate he removed from one of his tanks. he said he was going to sell it anyway, and that it was choc full of bacteria. I got a good deal for it I suppose, but did I luck out or crap out? It was very dirty, and smelled of eggs ([probable the Hydrogen sulfide). The water got awfully murky, a greyish green colour after I filled the tank. Why would he throw out his substrate (aragonite sand), was a chump to buy? Can I save my tank?

[ChrisRD]

If the return pump is getting ahead of the drain, you need to use a larger drain, or put a valve on the return pump so you can dial it back.

An overflow setup will help, and in fact, is a must (unless you drill the tank). They are rated for a certain amount of flow, so get one that will handle what your return pump is putting out.

Adding sand from an existing system is a good way to get a new system seeded with bacteria and critters. My recommendation would have been to setup your system with new sand, and just use some of the old stuff you got locally on top of the inert sand, to seed it.

HTH