My hot tub is losing water. It is not evaporation. I put about 35 gallons in last night and this morning the level had dropped 2-3 inches. Besides a crack in the shell (which is possible but is not visibly seen) what other ways could it be losing that much water? If it is a crack, what do you do?

Can you see around the base of the hot tub, is the ground or slab wet. You can easily lose this much water every night if your pump seals are bad or any hose clamp is lose near the pump. You have an inspection door, remove it and run the tub on full speed.

I found my leak at the filter cap. The cap had a crack in it and while recirculate cycle came on, the press would cause it to leak. I hope you already have it fixed, but if not, maybe this will help.

Why would you pay $750 to replace a cracked filter cap?

I just fixed my Spa today. I had been losing about an inch of water every couple weeks for a few years. But I would just fill it up. At first (when it was maybe 1/2 inch) I thought it was just normal evaporation but I did notice that the concrete was a little wet. What I didn't realize is that the frame underneath gets wet and the wood can start to rot so don't leave this go too long. I went out there the other day to check the level and the Spa was almost empty. The fitting that went into the heater motor corroded away and the water just poured out. The point being your SPA can almost completely empty itself from a corroded connection or leaky hose. Take the sides off your SPA, in my case as soon as I added water I could see the leak. If you are not losing a lot of water then run it and check for leaks you will likely find a bad motor or fan seal.