Almost had a flood - need a dummy sensor

Hi Goody,
Here is what I use for auto top off.
Aquarium Specialty

 

Thanks bulltrader. I went ahead and started looking on the Internet and saw this one as well as some others, but too expensive right now. I'm just getting into the hobby, so maybe I'll stick with adding my water by hand. I did find some DIY topoffs, what do you think about these? Melevsreef.com - Automatic Top Off System

Also, am I right that the water being used to topoff your sump or tank is regular freshwater (ro/di)? If so, how big of an affect does this have on the parameters of the tank?

This leads me back to my question earlier on if I should not use the ro/di system I just bought, but get the free seawater:-/. Then my topoff would not change my parameters, right?

 

goody, your top off should be ro/di water NOT saltwater. As your water evaporates it's leaves the salt behind and will increase the salinity but if you top of with straight RO water it will keep your salinity constant. When you do a water change then you use saltwater. Your parms should stay stable.
The DIY topoffs look good.

 

Wow, I didn't think about that. What is weird though is that I've been adding a little premixed saltwater to my sump due to evaporation, but my salinity is always right at 1.024-1.025 Could this be because I am adding such a little amount?

I am new and I am adding water about every other day because I am worried of water level in sump going to low. I know I should get a bigger sump, but right now I am going with one I have, which I believe is only 12gallons, but is rated for a 125gallon tank. I am looking into an old 20-30gallon tank that I can use, but in the meantime, I am wrong in adding less than a gallon of premixed saltwater every other day?