Has anyone got any experience or links to forums where people are pumping water between 2 tanks, without using overflow boxes or drilling. The 2 tanks I'm considering are at different heights. One is a nano and it would be much easier to keep it stable by using the water from the other 350L tank.

I'm considering running 2 pumps and rigging them up with float switches and inline solenoids to prevent a siphon effect. I think it would be too risky to have them both running at the same time without float switches.

Considering 2 possible ways of rigging it up.

Sequence 1:

Nano tank pump turns on, drains until a float switch in the nano tank detects the water level has dropped to a pre-defined point.

Nano tank pump turns off.

Main tank pump turns on, runs until a float switch in the nano tank detects the water level has raised to a pre-defined point.

Main tank pump turns off.

Repeat.

Sequence 2:

Nano tank pump turns on, main tank pump turns on.

If water level in the nano tank hits upper limit float switch, turn main tank pump off. Turn back on when it drops below again.

If water level in the nano tank hits lower limit float switch, turn the nano tank pump off. Turn back on when it raises above again.

I think to make sequence 2 work, I'd need 4 float switches, otherwise it might be too sensitive. Lower limit (for turning nano pump off), lower limit but a little bit higher (for turning nano pump back on). Upper limit (for turning main pump off), upper limit but a little bit lower (for turning main pump back on).

Why don't you want to use an overflow? That's the simplest and most reliable way to do it.

Will this be for marine or freshwater?

Don't want to use an overflow because I can't fit them on either tank ... well not without cutting out the lids. Asthetically, it wouldn't look too good.

Initially freshwater, but if I can get it working, I'll put the nano back into marine. I have a large freshwater and large marine tank running at the moment in the room.

Something like this? viewtopic.php?f=28&t=52072

I have remade this in 20mm pressure pipe, but could be done in drain/waste pipe or conduit

Maybe, I'll have to have a think how that might work for my situation. Not sure I want to rely on a siphon though, as the nano tank will end up with no filtration at all with whatever system I put in.

Here is the 'hard' version:

laid flat (tank glass goes in the middle):

Very compact, had this running on the hillstream loach tank