Just bought a house with a 18x36 pool and trying to start it for the first time.
Here in Quebec, Canada, it seems pentahydrated copper sulfate is becoming popular (see: http://www.crystallineh2o.com/EN/index.php). I saw here some advices against copper sulfate, but nothing about the pentahydrated one.
here is a list of pools using pentahydrated copper sulfate. It made me buy a bottle of this product.
That was before I found this forum.
Now I figured out I may not need this product and only buy bleach and baking soda with a good test kit (just ordered taylor k-2006C). Anyway I already started using crist. H2O so I may use up the bottle before switching to BBB method.
So far what's happening with my pool in the first week of opening is that I opened it the cristalline H2O way: put a bit of the product with some chlorine in powder form. did also a shock treatment with a bottle of shock powder (sock it HTH). Ph was a little high, so I added a bit of ph minus.
Result is that my water is perfectly clear. Ph is perfect (7.4) total hardness too (250) alkalinity is a little low (45 or 50). Tested with paper strip so I still don't know the CYA level.
The only problem is that my chlorine seems to disapear really fast. Cristalline H2O instruction tells me to maintain chlorine level at 1.5 the first week and then lower it to 0.8ppm at all time. But now when I put chlorine at night, a few hour later it is at 4. The next morning it's still at 4, but around noon it's already zero even if there is no sun... I also noticed some grey deposit at the bottom of my pool. I then wait in the evening to add chlorine everyday with the same results. The water is still perfectly clear at all time though.
Can't wait to receive my k-2006 to test for CYA. Maybe it's the culprit.