Do It Yourself Dye Test
If your pool has a crack that starts in the tile and runs down the wall you can test for a leak without having to call and/or pay a service company.
Below is a quick video of a crack on the wall of a plaster pool, I tested this without getting into the pool. You will notice that just inches below the waterline the crack shows leakage. You can do this yourself and test as far as your arm length allows. Not all cracks leak, I’ve seen very long cracks not leak and very short or small one that leak a ton. Most crack may only show dye pulling along one or two points, so you may see signs of leakage at one point and two inches away it may not show, or pull, at all.
You will need dye, I use the phenol red from pool test kits. I buy the single bottles from pool supply stores, even supermarkets have it in the hardware and pool section. Cost about $2.00. If you use the one from your test kit you’ll need to replace it before testing water chemistry levels.