After a successful 1st season using the TFP advice and system, we noticed we were filling the pool a bit more than we were at the beginning of the season. I closed the pool and after turning the pump off for the season (we ran the pump 24/7 during the summer), I found the pool level dropped very quickly - lost 3-5 inches within days, and dropped down to below the bottom step by the end of winter. So I reopened pool - hubby cleaned out and regrouted steps where we thought there might be a leak, refilled & started the pool back up. It's sparkly and clean, but still losing water. I've observed that when I am running the pump, the pool leaks little or not at all, but when the pump is off like it was last night - the water drops fast - at least an inch since last night. So where to start?

Do you have a main drain?

If it doesn't leak when the pump is running, but does when it's off, then that points to a suction side leak. Do you see air in the pump strainer basket when the pump is running?

If you have a main drain and/or more than one skimmer then you isolate them one at a time and see if it makes any difference.

Trying to get my head around this - the water dropped after the pool was covered for the winter all the way to the last step. We have one skimmer and obviously it dropped way below that. So my thought would be main drain ACK. Seems like that might be very expensive.

Do you have a light? If so where was the water in relation to that?

No light, one skimmer, 2 returns, one main drain. Water drops to below the first step - we have 4 steps. I find when I vacuum if I have it set to waste I get good suction the whole time, if I set it to filter the vacuum suction fluctuates.

Did it stop at the first step? If it did then you need to look for a leak in the suction piping at that level. Maybe near the equipment pad where the piping comes up from the ground. I assume you've looked all around inside the pool at that level.

MORE SLEUTHING!
I'm a teacher so I've just now had time to methodically look at some stuff. Last year I think I ran the pool with 95% TFP advice and 5% luck, so this year I'm trying to become more of an expert! The pool is still losing water when the pump is off. I played with the 3 way valve - I never did fully understand it last year - so maybe you guys can help me put all these pieces together.
Photo shows valve in the normal operating position - suction is normal from the skimmer and pressure is constant @ 15PSI.
If I turn it so #2 is off - pressure stays @ 15PSI but there is no suction from skimmer hole.
If I turn it so #1 is off - pressure flucuates from 15PSi to 0PSI and so does suction - I figure this means air is getting into system.
So is #2 the main drain and #1 the skimmer? And then does this mean air is coming from main drain?


Oh and I named the pic multi-port - but I guess its a three way valve - ooops

I had to read it a couple of times but it appears that when you're drawing water through #1 the pressure stays steady and there's no suction from the skimmer. If this is correct then #1 is your Main Drain.

When your drawing water through #2 the pressure fluctuates. This is the skimmer line and appears to be sucking air.
There a few common causes of the skimmer sucking air without having a leak. Let's attack those before we go hunting a leak.
1. The skimmer weir is sticking causing the skimmer to draw in air. Make sure the weir operates freely.
2. The water level is low causing the skimmer to suck air in. Raise the water level to between 1/2 and 3/4ths up on the skimmer face.

If those don't fix the problem then we'll start looking for a leak.

Skimmer weir is not sticking, I raised the water level to 3/4ths up on the skimmer face (it was already above 1/2), turned so that only drawing water from #2 and still same problem - here's a picture of the bubbles coming out the return jet.

Have you purged the air from the filter since raising the water level? Also check the pump lid and make sure it is snug.

Also when looking in the top of the skimmer can you see a vortex when just pulling from the skimmer.

It's beginning to look like a skimmer line leak but we need to rule out other things to be sure.

When just pulling from the skimmer every 45-90 seconds you can hear a sucking sound feel the suction get stronger in the skimmer and then see a bit of a vortex, then pressure drops, returns don't shoot out with hardly any pressure, and there is little suction from the skimmer. This cycles like I said, about every minute.

That almost exactly describes a sticking weir. Are you sure it isn't hanging occasionally?

Weir not sticking - the pressure loss happens even if I hold the skimmer weir open

You could be sucking air in the skimmer plumbing somewhere which would explain the water loss when the pump is off.

Try this; switch the valve to pull only from the main drain and plug the skimmer pipe in the bottom of the skimmer with either a winterizing plug or a foam ball and see if the water level drops. If it doesn't then there's a leak in the skimmer line. You'll have to shut the pump off to make this test valid as it doesn't leak with the pump running.

Plugged the skimmer pipe and shut off the pump a couple of hours ago - pool's not leaked at all -

Should I be afraid?

Be afraid, be very afraid! Ok just kidding.

A leak in the skimmer line might not be that bad to find and fix. I'd start looking where it comes out of the ground near the equipment pad.

Hubby dug down about a foot away from the pump and filter just to see how deep the pipes are buried - didn't see any water or excessive dampness. With the amount of water the pool has lost this winter and then in the past month or so I've refilled about a foot or so of water twice, shouldn't there be a damp place in the ground somewhere? Seriously, where IS all that water going??!

I can almost guarantee the water is departing via the drain. Plug it in the pool with a rubber plug and valve it off at the filter.. When you replace the liner, you can repair the drain line. That should stop the leak.

Scott