Please Help me solve this Problem

[darknessheir]

So I have had my 75 gal with 20 gal sump set up for maybe a week with water, just to monitor flow and evaporation. Working on getting all the stuff set up under the tank. Heres my question! I am experiencing about a half gallon per day evaporation. I have to sump set up that if the overflow were to break the return pump would only suck up the water in its section thus not flooding the tank. I want to add an auto top off system but the sensors would need to be in the return section. If the syphon broke and the pump drained its section the top off would kick on, fill the compartment, and essentially flood the tank as it kept filling and draining. So would it be a good idea to put the top off on a timer so it can only run for like an hour each day, just enough time to fill the evaporated water and then shut off when its full or the time runs out. Other wise do any of you have any other ideas where the top off sensors could be located. I might get a piece of glass to go over most of the sump to lessen the evap.

Can anyone recomen a good DIY top off or a good one to buy?

If I do put glass over the sump will my micro/macro algea I plan to put in the ref still benefit from the light if there is a piece of glass between it?

Also can I add a small Metal Hallide light over one section of the tank to lighten up one area so I can have some more light needey corals and an anemone?

Thanks in advance

[melosu58]

Moved to the General Hardware and equipment discussion.

[darknessheir]

Sorry about putting it in the wrong section. Any one help me out here?

[dropin]

under the general premesis that when the syphon breaks it is because of a power outage, thus the pump would stop and the auto topoff would also stop. so no filling, when the power comes back on , pump starts and if the drain from the main tank is a u shaped type, you would get flooding, a internal drain starts and no flooding, a glass top on the sump area is not a good idea, you need that oxygen exchange. and the mh light on one side wouldn't hurt, but, it might be better to put it in the middle and allow the spread of the light ( about 3 feet per mh) to light the whole tank.