I'm still a newbie - we have had the house with pool just over a year, and I am still learning about it. Our pool has a spa that flows into it. We run the filter from 8 to 5 daily. At night, the spa shows a considerable water drop (like 7" for the 7' diameter spa) - which is then replenished each morning with the float water filler. I'm not sure whether this water drop represents the collective evaporation loss over the entire pool + spa surface area, or just the spa. So, I'm unsure about how to do a bucket test for evaporation, and whether to focus on the spa or pool (or both) for leak detection.

I'd appreciate any guidance/pointers/advice from all of you more experienced pool people. Thanks.

That doesn't sound like a true leak, though that is remotely possible. That is almost certainly a valve not closing correctly somewhere. There are two possibilities. By far the most likely is the check valve on the spa return. It is also possible that the three way valve on the spa suction is not fully closing.

Is there a way to know which is the check valve on the return line, or to test this?

Hopefully your check valve is designed to be serviced. If so, and you can find it, you open it up, clean out any debris, and replace the flapper if it looks damaged.

If you can't find the valve, post a picture of your equipment pad and we should be able to point it out to you.

Here's a picture. How do I tell which one is doe the spa return?

That gizmo right in the middle of your picture just above the dirt (with the clear cover and the 8 screws on it) appears to be a Jandy check valve (and is probably the spa bypass line). Inside it is a spring loaded flapper valve that prevents water from going backwards (in this case upwards). If you see any **** in there, you can remove the screws, pull the cover and clean out the valve (don't screw up the o-ring)

I agree with Q but it'd be nice if you could take a pic so we could see how the discharge of the filter is actually routed. It's hidden behind the tablet chlorinator and plumbing now.

Here's a more top-side view, from the right and left. The chlorinator is not used - just the SWG.

That helps a little.

On the left side of the bottom pic (Between the heater and filter), does the bottom of that 'Tee' go anywhere or is it just capped off?

Can you tell us which way the actuated valve goes when in pool mode?

Ah hah! Good question. It is blocked off. Now the flow makes sense to me.

What do I need to do before or after I take the screws out of the check valve to inspect it ( other than turning off the pump)?

There are still some unanswered questions but they're not important right now.

Just look for debris caught in it and/or a nick or tear in the seal and flapper or gasket.

Ok, thanks. I am out of town now, so the diagnostic work will continue
when I return.

Valves are currently in pool mode. The capped off "tee" is to support the plumbing and the intellichlor I guess there's no need to worry about freezing).

Nice job of plumbing in a restricted place. The only thing I would like to have seen on it is valve to regulate the amount of water going back to the spa while in pool mode. Right now half goes to the pool and half goes to the spa.

System was probably originally put in without the intellichlor.

OK, back in town, so I can look at this problem now.

What do I need to do before or after I take the screws out of the Jandy check valve to inspect it ( other than turning off the pump)?

Nothing special before but I'd lube it real well as I put it back together.

Pulled the valve cover off, and inspection showed no debris - so now I'm really mystified.

When you inspect the check valve, look closely at the flapper, rips or tears (don't have to be very big) can cause this problem.

You can also inspect the two three way valves (the valves with actuators on them) in similar fashion. Remove the actuator (4 screws) then pull out the diverter body (the remaining 4 screws). Look for crud keeping the valves from closing entirely. Additionally, those valve actuators can get out of adjustment, not allowing the valves to totally isolate the two bodies of water.

To test, with the valve actuators removed, place the valves in the appropriate position (with the proper ports closed) and leave it overnight.

I replaced the spa return check valve , and that did solve the problem. On closer inspection, there waz a tiny tear in the old one.

Thanks for all your help.