SPA Drains by itself

[Cray]

I have a 20K gallon in ground pool/spa spillover. Around 2 weeks ago, I noticed that the water in the spa was lower than normal and the jets would come on but with very weak pressure. I added water to the pool but did not retest the jets. I go out of town for 4 days and when I return the SPA is drained to below the jets. So I turn the valves to spa fill mode to allow water to flow from the pool back into the spa. This fills it back up to the normal level. About 6 hours later the water in the SPA has leaked out again. I tested to see if the water was flowing back into the pool but it was not as the water level in the pool remained the same. I checked around the pool and around the pool equipment area for soggy ground. There is no sign of water leakage from the filter pump, etc. Does this mean that I have an underground leak and what is the average cost for detecting and fixing such a leak?

20K gal, IG Tahoe Pebble, Jandy Stealth Pump 2HP, Jandy Cartridge 460 Filter, Jandy Aquapure SWG, Polaris 3900 Cleaner

 

[zea3]

Hi, welcome to TFP! Look for a check valve on the plumbing line going to the spa. It may be stuck in the open position allowing water to flow back into the pool. Unless you have an enormous spa, you will not see a noticeable change in the pool's water level if it flows back into the pool.

 

[Kiss4aFrog]

Welcome to the forum

Since they share the same water if the spa is actually leaking to ground then you would need to add water to the pool. If you haven't noticed the pool water level dropping it's likely the spa is just leaking back into the pool and as outlined above the check valve is a likely culprit.
If the valve is stuck partially open you might be able to hear it leaking. Fill the spa and shut down the pump and listen to the check valve for any noticeable water movement noise through the valve.