I recently became the owner of a pool and "spa," but the spa is a bit strange (it's just a tiny ~300 gallon fiberglass tub alongside the pool), and I haven't figured out how to actually get it to filter along with the pool water.
The pool and spa are on the same plumbing system (one pump, one filter), but currently the suction and return valves for the spa are shut off, so only the pool is being filtered. This works great for the pool, but I'm trying to figure out how to incorporate the spa into the plumbing system.
The problem is that when I open the suction and return valves for the spa, water circulates but the water level of the spa starts dropping (i.e. I must be sucking more than is being returned). It seems to drop indefinitely (it'll continue dropping well below the pool's level). If I turn the suction valve so it's only partially open, I can get the spa to almost maintain its level, but over the course of an hour, it'll either raise or drop by an inch or so depending on where exactly I have the valve.
So my question is basically: how is this supposed to work? In particular:
1. Can I somehow get the spa to maintain its water level while both the pool and spa are being filtered?
2. If not, am I supposed to just filter one at a time and not both? That would make some sense, since you'd probably have them at different temperatures normally (though I have no heater in the system for either the pool or spa)?
3. If I'm supposed to only filter one at a time, how would I do that automatically without having to turn valves constantly to change which one is being filtered?
One other potentially relevant piece of info: The system initially included a solar heating array on the roof, but it's been defunct for a long time.
I'd also be curious if anybody has any other insight into my system. Have you seen a tiny "spa" like this before? Is there a name for it?
My Pool and Spa: