Overflow box frustrations

I have a reef ready tank that I'm using as a freshwater planted tank. I have a canister filter setup on the overflow, the intake is inside the box and the output goes up a PVC pipe and through the notch in the side into the tank. All is well in general, but I've run into some issues that I'm unsure how to resolve:

1. I can't fill the tank all the way to the glass brace as I would normally or the water level in the box is even with that of the tank and I don't appear to get the effect of drawing surface junk into the box and down to the filter as I would like. If I lower the water level I can get the level in the box to be lower than the tank and achieve the desired overflow effect.
2. I had the auto-fill sensor outside the box initially, but discovered that the water in the box could drop to zero without kicking on the auto-fill switch. I moved the switch inside the box and it seems to function as desired most of the time.
3. When performing a water change, if the water level drops below the overflow inlet, the filter can pump the box dry in a matter of minutes. This is bad as I put the heater inside the box. It's a metal tube heater which doesn't have an internal thermostat and relies on a temp controller. I had to put the thermometer outside the box because it would kick off too soon as heating the water in the box was much faster than heating it in the entire tank.

The last item is the biggest problem. Short of remembering to turn off the heater and filter prior to lowering the tank water level, it is a real problem. I have considered drilling one or more holes in the lower portion of the box just in case, hoping that it would generally draw from the top most of the time. I have also considered installing a fixed siphon from the bottom of the tank to the bottom of the overflow such that the overflow box will retain the level in the tank at any given time. But again, I would want this functioning only when the tank level dropped as a result of water changes, but I think it would function that way automatically. It just seems like there should be a better way, Am I overlooking something? It does have inlets lower on the box, but they go into a small space that is open to the top and relies on the motion of the overflow water to also siphon water in from these other inlets. So it doesn't help me in this situation. I'm thinking the permanent siphon is the best option unless someone has a better suggestion.

Michael

 

No, there is no sump, but the concept - and really the problems - remain the same.

Imagine that I had a sump and I did a 20% water change. The water level in the tank would drop below the level at which it can flow into the sump. The pump wouldn't know this, so it would continue to pump water back into the tank until the sump ran dry. If the heater was in the sump, it wouldn't know it was dry, and because the thermostat sensor is now exposed to the 70 degree air, it will kick on and overheat.

I purchased a relay today at the electronics supply place and will build a system where if the auto top-off system kicks on because the water level dropped, it will disable the pump and heater until the water level is restored to normal levels.

Michael