Not likely to be a crack in the shell but there is a leak. It may be a motor seal, gasket, or plumbing and does need to be checked out.

Cold air just makes the evaporation more visible when the top is off. It doesn't speed it up.

Scott

Thanks Scott!! I will get my repair guy out to look @ it! i am so relieved that it's prob not the shell... :) Whew, what a learning curve!
Erin

I don't have a tub, but cold air has a lower dewpoint, ie it is drier. It will suck up moisture more quickly than than warm moist air. SCIENCE!!

The delta is minimal at best.

Scott

Please pardon my ignorance, but what is delta? My repair guy can out yesterday and only found 1 small leak...he has repaired that and also caught that one of the air jets below was blowing out directly on the motor ( told ya'll I was still learning). He also fixed that. Now we will wait and see how the water level does...maybe it was a combination of the small leak and cold air. Time will tell.

Delta is a change.

Scott

Busboy,
You are right in the fact that temp does effect evaporation. But it is the air movement over the water that causes the most evaporation.
Ladybug says she uses a cover so that air movement would be minimal, even if it leaks a little.

Would not there be a puddle of water on your patio if that much water leaked in just 3 days?

It's funny you should ask that stateguy...I have looked for puddles...the hot tub sits on the deck and as far as I can tell, there is nothing pudding under the deck and there are no signs of water on the deck.
I am really getting frustrated too. My repair guy was out Friday and took the panels off and look pretty extensively from what I could tell. I went to check water levels last night and it's STILL LOSING WATER. ARGH! I've studied the shell inside and can see no visible cracks....could it be leaking through one of the jets maybe? But then we should probably see that when looking at it with the panels off?
Sigh. I am at a loss. Will be calling my repair guy to come back out today. :(

What is the surface that the tub is sitting on?

Scott

the deck

Evaporation rates are primarily dependent on water temperature and dew point temperature. The larger the difference between the two, the higher the evaporation rate. However, the cover should stop most of it but it depends on how many hours of the day the cover is off the spa.

I don't know where the OP lives but in Chicago with a 100 degree spa would lose about 0.025"/hour due to evaporation when uncovered. With the cover, it shouldn't lose much water at all.

Here is a link that might be useful: Evaporation Study

ladybugfruit,

And that is made of what? Concrete, pavers, wood...? My point is while not seeing a wet spot may seem to be a question, if the water leaked through the bottom panel, the spa may be hiding the wet spot if it can drain over a porous area.

Scott

mass, I am in Texas..hardly cold enough ( 25 degrees one day, 70 the next these days) for that much evaporation I would think.
Scott, ah, wood deck... I have tried to look underneath to see if it's leaking through but it's a bit awkward and hard to tell. Booger has got to be somewhere! And I haven't even bothered checking the chemistry because I can't keep up with it. As soon as we find the leak though, I am going to drain it and start over on that front ( btw, LOVE the pool forum that someone here directed me to, that uses the BBB method).

I have a frozen ring around my hot tub and am loosing water. I topped it off about 2 weeks ago but it is low. When I turn on the jets it causes the intake to gasp. I just replaced my cover and guessed a little large on the diameter of the cover, about a 1/2 over all around, could this be the culprit? I see a few icicle drips down the side but mostly a ring on the ground around the tub. The weather has been extremely cold lately.

I think you diagnosed the problem. It sounds like the cover is too big. You are probably losing water (as vapor) around the fold in the cover because the shoes are not fitting correctly.

A cover should lay flat, and seal to the top of the spa. They do NOT seal against the side. If anything, an over sized cover should seal better, being that it's a little bit heavier. Now if the top of your spa isn't flat, or the cover is slightly warped (not that uncommon), any cover will leak. Try putting something weighty on each corner and see if that solves the problem. Also, your cover tie down should be attached snuggly....and there we go, with a response to a 4-1/2 year old post :)