zero hardness

[chem geek]

Two comments. First, I don't think your measurement numbers are correct. It is impossible to have a TA less than around 30 ppm with a CYA of 80 ppm and a pH of 7.8. So one or more of these numbers must be off. Did you mean 120 ppm for TA (that is, 12 drops to make the color change)?

Second, if you use calcium carbonate flakes to add calcium, then this will raise the pH and TA way too much. What is needed to add calcium is calcium chloride pellets. So, assuming the Calcium Hardness (CH) measurement was done correctly, then it's Calcium Chloride that needs to be added. If the Total Alkalinity (TA) is truly low, then baking soda can be added to increase it.

You should probably get yourself a good test kit, the Taylor K-2006 you can get here for a good price or the TF100 from tftestkits.com here that has 36% more volume of reagents for tests so is comparably priced to the K-2006 on a per-test basis. It's hard to lower some water parameters once you've added them (like CH and CYA).

CH doesn't just go away, so did you have some last year when you closed the pool and if so, how much? The only way CH would drop is through dilution so unless your pool had a leak that pretty much emptied/refilled your pool several times over (with continuous dilution), then the CH should have held. Did you have a serious amount of rain with overflow of the water or have you noticed a significant water bill over the winter? I'm guessing that the CH test may just be off (wrong). Even fill water usually has some CH -- my own tap water has 50 ppm, for example. To verify your CH test, try testing your tap water which should not have zero CH unless it truly is soft water (or you have a water softener).

As for the green pool, it sounds like algae -- chlorine will be needed for that, but with so many water parameters out of whack and questionable you really need to know what's really in the water first. Keep the chlorine level up in the meantime to keep the algae at bay (and with high chlorine levels the pH test won't be accurate and will tend to seem higher than it really is). I'd have you shock with chlorine, but I'm not confident of the CYA number. Since this isn't a vinyl pool, I suppose you could just hit hard at 20 - 25 ppm FC and see what happens (the algae should go from green to gray-green, perhaps within an hour, if you're adding enough chlorine). See this sticky for encouragement.

Richard