I shouldn't laugh but sorry, I am. I've been there. That's why. I recently installed a bushing in the "end of the line" in the pipe in the sump. It's almost as risky as a valve but there is a smooth taper between sizes.I figured there's an equal if not greater chance of a blockage prior to it. It helped a bit. Is your water inlet submeged ? Hard to explain...Is water entering the pipe below the water surface area ? It sounds like there's a problem obtaining the correct "vacuum" required. :?
Something I've modified might be worth a try. Instead of drilling different size holes in the "dry portion", I installed a reducer bushing there and extended 1/2" pvc further way from the standpipe. I then installed a nylon 1/4 compression/1/4" pipe thread adaptor into the extension. An airline pushed in a drilled end cap will work also. You can then adjust the "vacuum" by restrictig the airline which will in turn raise/lower the water level in the overflow area. This will also increase the time frame for cleaning salt creep which will eventually decrease the size of the hole originally drilled.
Who knew there were so many "trades" involved just for fish eh ? "Surround-sound" is still another option :?
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Doug
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