ok that makes sence.. i don't have alot of evaporation but it would be nice to have it done for me automatically... water changes too

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What to do today, water change?

Its easier on the tank to do frequent small top offs rather than one or two large top offs per week. An autotopoff is a very handy piece of equipment and can be anything from a $10 float valve (which i don't recommend) to soleniods and electrical or magnetic float switches and even optical or air sensors which are extremely accurate. I use a solenoid and float switches on my top off reservoir to control my RO/DI system and an air sensor type to control the level in my display and sump.

There are lots of good vendors that can supply kits or ready made systems.

i think i bought my solenoid ready made kit for about 90 bucks however you have to take into consideration the RO/DI unit will be another 100 bucks or so.

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You won't get a reef quality RO/DI worth a hoot for $100 but for about $150 you can including things like a TDS meter and pressure gauge.