
, Put poly-fil on top as a pre-filter.
If you put the filters in PVC pipe, cross-drill with very large holes for flow.
Set the first heater temp where you want the water, second 2*F lower and the third 2*F lower than the second one. This give you a better chance of the first and second doing all the work and the third acting as an emergency heater and still staying with-in a 4*F range. Unless you have a high heater requirement (ie water to air temp ratio).
Dr Joe
.