Deb - have you tried just getting a long board and putting on the bottom of the tank on one end, and over the side on the other diagonal like? That way no matter at what level the water is at, there's always a ramp for critters to climb out. We use this for amphibian traps so that if a mouse or shrew gets in by accident, they can get out. Just an idea that you probably tried.Tank setup for the horse is a 110 gallon plastic tank.... Filled to the brim in order to keep other critters from drowning in it.... Sigh IF they can get to the edge and grab hold they can get out.... First year I didnt have this set up and I was drowning a rabbit a day.... so sad.
The fish survive totally on what the tank grows or on what insects drop in.... AND what my horse delivers to it through back wash. Horses will drink their fill and on the last sip will open their mouth to rinse out thier toofies. because that water will have alot of green organic material in it. The fish start out living on that..... After that I am careful not to scrub the sides of the tank too hard while cleaning it out. Fish are incredibly adaptable to their environment. They rarely grow larger than their tank of water will support especially if you change the water only on occasion. My fish will get about three inches long and stop growing. So there is enough food in there to support about four fish....
The tank setup is simple.... Tank and tank valve
These are very roebust and as a matter of fact I also use them for chicken water....
deb