I have had a slow leak in my pool for the last three years since I bought my house, and I am about 90% sure that the leak is in my underground pipes (covered by rediculously thick old 4x4 ft panels of old concrete which I tried lifting up to no avail). I have been doing the bucket test with the filter 1/2 off and half on and so far I noticed that I
1. definitely lose more water than evap (1 mm loss in bucket compared to over 1 cm loss outside of bucket in a 24hr period)
2. definitely lose more water when the pump is running.
3. The pool holds water during the winter (when closed) over the point where the plugged skimmer, plugged returns, and light, are so I do not think it has to do with the shell.
I did a makeshift caulking job of the old single skimmer two years ago because there was some leaking from that, but my repair seems okay, so I have basically ruled that out (for the bulk of the leak at least).
I just had a new filter pump and multiport installed (I thought that might solve the problem if there was any backwash line leakage because of possible spider valve, etc. and, my backwash line runs underground to the street which makes it hard to see any leakage because I believe that there may be a break underground in that pipe somewhere before the end of the pipe, so if there was a leak out of that...I would probably nver know.
Anyway....I think my next step would be to call pool company or American leak detection.
I have been constantly filling the pool with water for the past 3 years and the leak is slow enough that I think (or hope) no damage will be done...but I am just getting sick of cold fill water and a higher water bill.
My real question is though...would there be a way to fix an underground pipe leak without having to lift up these rediculously heavy slabs of concrete. Eventually I plan on replacing the pipes altogether, and replacing the concrete with pavers but not $$$ yet.