float switch

[ReefVan]

whaase,

If you want something real dependable and rated for millions of cycles, get a pressure sensor switch World Magnetics PSF-100A 0.5 in. Can be bought through Digi-Key Canada.

This switch will actuate when sump level raises/lowers 0.5" and contacts are rated for 5 to 30 volts. You'll need a relay to reverse the contact cycle, but they work great.

How do you think the retail top-off units work? (Tsunami - Shhh!!!!!)