Accurately measuring evaporation for top-off?

[muppet]

How do you do it? By eye only? I've been using my SG as a guide, but that's not really too helpful.

My issue is that I've got one of those all-in-one's, and the chamber with the return pump is always a little lower than the DT area, and of course, adding water to the pump chamber isn't all that predictable, because some of it ends up in the DT, not all, etc. Using the pump chamber alone as a guide isn't that reliable as I can't easily predict the effect on the DT level.

I imagine those with full-blown sumps have a similar problem.

How do you ensure accurate top-offs when your tank exists in various chambers whose levels are constantly effected by pump throughput and differing water pressure?

[snarkes]

I basically have it where there is a line marked in my sump that notes the level I want to maintain. All I do is keep it there when I add water. Could be easy enough with a cheap ATO system.

In my nanocube, i just eyeballed it. Didnt have any problems for the 3 years I ran it.

[chuck116]

Plus ! with SNARKES a mark in the sump on the bigger tank and in the nano I top off the the elbow where the inlet from the pump goes to the tank.

Good luck CHUCK P