How much water is normal to lose to light use & evaporation?

[mitchryan912]

I'm not familiar with the Triton TR-60 sand filter. Does it have a multi-port valve? If so, perhaps the spider gasket is damaged.

Yes it does, and that was the problem. One of the "spokes" between the filter inlet and the waste outlet had slipped out of the groove it rests in, creating a small gap for water to leak out of. Glued it in place, let it dry, then greased it up. Works fine now without any leaks.