Weird hot tub issue

A couple of weeks ago my wife noticed that the water level of our hot tub had dropped several inches. I checked the pump, control box/heater connections as well as the perimeter of the tub to see if I could find a wet area but no luck. We’ve been monitoring it and haven’t seen any further water loss. 

Tonight we  we were in it for about an hour and it lost about 2”. At first I thought it may be leaking from one of the upper jets but the loss continued right on past their level.  We didn’t have the main pump on so just the circulation pump was running. This pump runs 24/7. What changed by us getting in other than the water level going up? I’ve refilled it because the pump started sucking air when we got out. I’ll watch it for the next few days and see what happens. It’s the type that was spray foamed after the piping was installed so it isn’t simple to trace the lines out.

In my personal experience, it is the pump head.  I've gone through a couple of them.  Anyway, the water is leaking out somewhere, you just need to find it.

So the water level dropped overnight below the intake. There are no leaks at either of the pumps or the control box so I guess I have to start digging out spray foam to find the leak. I wish there was an easier way of finding out where the water is leaking from.

Is it possible the drain stopper is not sealing?  

Drop some food color dye in the water. Hopefully there is no ill effect on the tub itself but hopefully it stains the foam on the underside to find the leak.

For the record, "Leak" is not a weird hot tub issue.  That's kind of a normal hot tub issue. 

"Neighborhood  midgets wrestling in Jell-O who refused to leave my master bath". Now THAT would be a weird hot tub issue.   

How old is it?  Our first one went about 12 years before I gave up chasing leaks and got a new one.  With the old one the heater did fail in the middle of winter and froze some pipes.  I fixed the damage from that, but I think other pipes were weakened and I spent the next couple of years chasing new leaks until it just wasn't worth it.

It doesn't sound like a leak. You are loosing too much water for there to be no evidence of leaking. 

I think the stopper is not sealing, and all the water you are loosing is going down the drain. 

In reply to SVreX :

I think he is talking about a stand alone hot tub and not an indoor plumbed-in whirlpool tub 

In reply to dculberson :

Hmm... maybe you're right. 

Still has a drain, right?

Sorry. Just to clarify this is a stand alone outdoor 6 person hot tub. The fact that it’s leaking isn’t weird. The fact that the leak comes and goes is weird.  Since refilling it, a couple of days ago, the water level hasn’t dropped. I’ve never seen a mechanical system heal itself so I have to assume it’s going to suddenly drop on me again. It’s about 10 years old so it may end up being replaced at some point in the near future.