Autotopoffs, or ATOs. Sanity-saving.

[Sk8r]

This supplies fresh water to your tank to make up for evaporation and to keep your salinity spot on. For the record, my 50 gal can evaporate a gallon a day, so five days can have the tank in trouble. An ATO is one of the first supportive gear items you will need to make life easier...including the ability to go on a vacation and hope not to have the Dead Sea salinity recreated in your tank.

Look for: how secure the sensor is going to be in your tank. JBJ makes a pretty secure one that won't come loose or move. It hooks securely on a provided strip that hangs on your tank.
Why? because if that sensor does not stay put come stray snails or ripples, you can get too little or too much water delivered.

You need an 'ato reservoir' which can be an old salt bucket (ask your lfs) or a spare tank. The ato sensor goes onto a wall of your sump and connects via power cord to a pump and hose in your ato reservoir. A low water level in your sump causes the float switch of the ato sensor to sink, sending power to the pump in your ato reservoir, which turns on, pumps water up to the sump, raises the water level in the sump just a tad, and all is well. A note: securing a sensor in a flat-sided tank is easy. In a round bucket, it's a problem.

The JBJ is a little complicated: you do not need to deploy anything but the (#1) sump water level sensor to make it work, but if the (#2) ato reservoir sensor could help you avoid a pump running dry, connecting both 1 and 2 is an option.

There are also many good brands. I've killed 3 Hydors, just sayin'. But they are dead easy to use.

Re why we don't stop evaporation: if you ultimately want stony coral, evaporation drives a kalk (calcium) feed, which arrives in bursts of fresh water. So it can be an asset: my 50 could grow stony coral like crazy. [I used Mrs Wages Pickling Lime [no kidding] for cheap kalk.]

[jmsilhy]

“How secure the sensor will be in your tank”

Sk8r this is if you don’t have a sump, correct?

When you do, all the ATO system goes in the sump, in the pump chamber, which is usually the first to go down in level from evaporation.

So to get this very straight, my reservoir is next to my sump, it contains the pump and rodi water (for now until I start dosing kalk).

The sensor goes in the pump chamber right where my good SG mark is, so that when water gets lower, fresh rodi will get pumped in until it reaches the good level again.

[Sk8r]

The ato can feed directly to a sumpless tank, but I don't recommend it. We are going that route, sort of, for our freshwater tank, where the water source is in the basement: we're going to punch a hole for a water line through an ac duct wall, bringing it through the vent in the main floor, so we can supply the ato reservoir in the base of the freshwater tank, which will have an ato feeding the actual tank. We will actively pump a limited amount of water from the basement into the main floor ato reservoir once a week, thus saving us carrying a 40 lb bucket up a flight of stairs every time we need a fill, and also from letting the water level drop in the freshwater tank. The marine tank is fed more conventionally, by an ato in the marine sump.