Aquarium Auto Top Off Fail safe

if (millis() >= 5000){

Rarely does this code actually do what the programmer intended. millis() returns the number of milliseconds since the Arduino was last reset or powered on, so that if statement is checking to see if it's been 5 seconds since power on/reset. Another thing to think about is that you are setting floatStatecounter, but never using it again. These two issues are related.