Just inherited an old pool and I have some issues I was wondering if I could get advice on. I'm not familiar with exactly how the main drains are constructed but this is a 1982 sylvan in ground gunite free form with 2 main drains connected together (proabably for safety). It has 2 hydrostatic relief screws on either side of the main drains and 1 in the shallow end as well. The problem is when I manipulate the valve to the main drain I can get air up into the pump basket or if I shut it down completely the main drain can bubble for a short time. Often the first couple of bubbles will be very large (maybe 3") and for a minute or so there will be finer bubbles. When I start the pump up, even with the main drain valve closed I get the same bubbles. If I wait for the bubbles to stop a minute and then turn on the main drain, I tend not to get any air or very little and the system runs fine. There's no evidence of water loss (i.e. level is staying precisely on the middle of hte tile line)... however we have had rain which could mean I am in fact losing water.
First of all do bubbles mean leaking? It would seem to me to be a relative certainty. Secondly since I saw the bubbles coming out of both main drain covers does that suggest that the air is in the plumbing between them and thus the furthest could be capped (even if it creates a less safe pool - I could always turn off main drain when swimmers are present but sitll get the circulation benefits otherwise). Has anyone ever dealt with anything like this? If it's not leaking much I might just deal with it. I need to replaster next year anyway. It's not looking to good at all.