[untamed]

Originally Posted by Tracey2

Thanks for the info, so when you do a water change you just close the valve to sump 2, empty sump 1 and fill again? So you don't have to shut return pumps or anything off?

Yup, that is exactly it.

As soon as I stop the flow between the sumps, sump 1 fills up capturing 50 gallons. As soon as it fills, I stop the flow INTO sump 1 and that sump is now completely isolated even as the return pump continues to run. (water just flows directly into sump 2 through the Herbie emergency drain).

I then dump sump 1, and refill it with new SW which is pumped in from the mixing tank. Then put the sump back into circulation. One advantage of this system is that I get to drain away any stuff that has settled in Sump 1 when I dump it. It is a good way to get rid of detritis.