water top off unit

get a 5 gallon bucket.
make a hole on top of the bucket for tube and connect that tube to top of your tank.

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you see that tubing? you just need to connect that tube straight to your tank
 
I use a 5gal container, a timer, and aqualifter pump. The auqalifter pump runs around $10 and uses airline tubing. It pumps a max of 3.5 gals a day. Perfect for top offs especially because you don't need to submerge the pump. This means if you dose kalk it won't deteriorate the pump as fast. I picked up a digital timer that has 24 on/off settings. Every 2 hours I have it come on for a minute. My tank loses 1/2 gal a day and 12 minutes of the pump running a day equals that amount. Later I plan to use a float switch, but this was fool proof and easy.
 
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