DIY overflow/siphon vs canister filter siphon

DeepDiver · Jan 31, 2019

All,
Salt water tank newbie with some basic questions. I’m in the process of sorting out how I’m going to set up the filtration in my 75gal FOWLR tank. My tank is not drilled and it is tempered. Right now I am between a Fluval FX4 and a sump. I’ve read plenty on the potential advantages of a sump although I am confident a canister will work just fine and is basically bullet proof if maintained. For a sump I would build a weir with dual siphon tubes.
My question is about the reliability concerns around a siphon feed for the sump. Canister filters are siphon fed and I haven’t seen or heard concern with losing that siphon. Why is this such a concern with sumps? Is the issue just with the pump continuing to run? How is a HOB overflow different, a siphon is used to get water from the weir to the external box. Can’t this whole concern be solved with a level (float or photo eye) switch in the DT controlling the return pump?

Thanks,
DD

Mical · Jan 31, 2019

The issues with sumps and overflow boxes and the GPH a pump can push. If the pump (after head loss) is too low, bubbles can form in overflow tube and there is the possibility of syphon loss. On the other hand a pump with too much flow can drain the sump to fast and overflow the tank. It takes some fine tuning IE: with ball valve on return to hit the sweet spot.

Re: canister filter - you'll get tired of cleaning it weekly and in doing so you lose alot of beneficial bacteria everytime you clean it..

Most folks here have drilled tanks w/sumps so the possibility of syphon loss is literally zero. Personally both of my tanks have HOBs with adjustable ball valves and large pumps and I'm diligent about flow rates. Sumps also add to tank volume, can hide equipment like heaters, skimmers, etc.

DeepDiver · Jan 31, 2019

Thanks for the response. So I need to match the siphon and pump flow rates. If the siphon tube(s) are in an overflow/weir that should help. As long as the siphon inlet is well below the weir inlet, as long as the pump is running, the siphon should not draw air.
If the siphon is compromised a photo eye or float switch should detect high water level in the DT and shut off the return pump. Am I off base with my though process?