Searching for a very slow leak

[mknauss]

Since the pool was new ( 1 year ago) I have had a very slow leak confirmed with a drop in the salt ppm and the CYA over time. Based on the salt loss I calculated a loss of ~20 gallons per day. We drained the pool this past week and pressure tested the piping to 30 psi using water - no leaks. The fiberglass shell shows no apparent issues. Our soil in this area is decomposed granite and thus water seeps away rapidly so no visible signs of water near or around the pool area.

We have no overflow but do have an auto-fill (we are in the desert). There is no line to waste, we use a submersible pump to drain the pool. No issues with floating the pool here - again we are in the desert!

So now I am at a loss! Are there any areas I am missing? We tested the spa system separately from the pool system.

Thank you in advance.

Marty

 

[borjis]

The spa system was completely isolated from the pool?

 

[gwegan]

Is there a cover on the pool? If not I would suspect evaporation. Twenty gallons is not much water. Can we see a picture? 5800 gallons is not a lot of volume. What is the surface area? Cover the pool with a tarp for a week and see if it continues to leak? How did you measure the twenty gallons per day?

 

[mknauss]

Yes - the spa system was completely isolated.
No cover. And not evaporation. We have a great deal of evaporation but salt does not evaporate.

Thanks for the input.

 

[gwegan]

Ok I'll beat a dead horse. With no cover you have some evaporation. In Nevada probably a lot. Cya can go down on its own over time.

Cover the pool with a tarp for a week and see if you have a loss. It may take longer than that.

 

[mknauss]

The reason I say that evaporation can be discounted is that the salt ppm of the water in the pool drops by about 100 ppm per week when at full salt of 3400 ppm. That comes from a seven week stint in mid summer where the salt ppm dropped 700 ppm with no use of the pool. Yes - there was lots of evaporation, but the salt should still have been there.

 

[gwegan]

Yes the salt should be there, I agree with that.

 

[duraleigh]

I know this doesn't help solve your issue much, but I simply wouldn't chase a leak (if it is one) that is that small. It's insignificant to the management of your pool and insignificant to your wallet.

I am not sure how you isolated evaporation from the equation (I don't think you can find a salt test to measure 100 ppm), but, to me, it simply would not matter.

After all that, I have to admit I often get overly-determined to solve something that is really bugging me, so, if that's the case, keep us posted.

 

[mknauss]

Financially you are probably right Dave. The issue is when we leave for extended periods the salt content drops and the SWG does not generate chlorine. I will have to 'train' a pool service we use to maintain pH and clean the pool on adding salt. As it is a small volume pool it loses enough salt ppm to effect the SWG in a short period of time (2 months).

The 100 ppm loss was averaged over a 7 week period. So we had a 700 ppm loss recorded over that time. The data was confirmed with a salt test and the SWG readout, which matched at the start and end of the 7 week period.

Thank you all for your input.

Marty

 

[pooldv]

The IC40 does not give a high salt error until 4500 ppm salt and it will keep making chlorine above that. Before I learned about cold water and false low salt errors I ran my salt level up above 5000ppm and it still made chlorine. So, you could raise your salt level to 4500 and still keep it well above the ideal salt level of 3400 ppm.

 

[mknauss]

I agree that I can start high in the range for salt to cover a couple months. However I also have to increase the level of CYA as it disappears at the same rate as the salt, and thus the amount of chlorine created by the SWG has to be adjusted based on the declining CYA ------ etc. It is a dance, but one that I most likely will have to learn!

I have been thinking about using a floater with pucks when I am gone for part of the chlorine load as the pool service personnel can handle adding those.

Thanks again.

 

[pooldv]

Good idea, that will help with the CYA also.

 

[mas985]

Have you checked all the penetration points (returns and skimmer)? For fiberglass, I believe they use some sort of gasket.

 

[banditig]

Mark might be right, my co-worker and I solved a fiberglass pool small leak at skimmer gasket by torquing the screws around the skimmer, we broke the tabs off the cover plate and had to buy new one though.