lbridges wrote:We agree a good set of test numbers is the only really valid starting place.
You seen to be a very rare sort, one with both a vested interest (the company link) as well as a willingness to help for free on a forum - so ask yourself - do you believe the pool store number of 93? It could easily be much higher depending on the test they are employing (I'm assuming turbidity). My personal test, and the one at my local pool store, has no numbers between 90 and 100, so 93???
The OP states the pool was shocked and 4 pounds of stabilized chlorine was added to reach an FC level of 7.5. With a CYA value of 93, the pool likely had insufficient FC before the lawn fertilization. And given the inaccuracies of the CYA test it could be easily be higher.
The fertilization might have tipped the scales toward algae given a too low FC level for the amount of CYA, but IMO something like Phosfree isn't going to fix it, and as far as I know there is no fix for nitrates other than drain and refill. And to fix the algae problem with such a high CYA value will take probably 50+ gallons of 6% bleach (corresponding number of liquid chlorine).
So ultimately I recommended following the advice at the link I posted as it was written a lot better than anything I could manage.
The CYA reading of 93 means they either tested the water using Aquachek test strips have really good eyes and guessed at the color "in between" the 50 and 100, or used a micrometer to get the value of 93 (ok, not a funny joke). It would be a good ideal they take the test again to make sure they receive a positive result.
We are on here to help the community solve problems. A lot of pool owners that visit this forum know who we are, so in most cases, we are just answering their questions before they have the need to call one of our tech's. We aren't a chain store looking only to make a dollar and that's what makes us unique. We don't EVER push anyone to buy something they wouldn't need. We are trained to deal with nitrates & phosphates, and do not sell Natural Chemistry because it is inferior compared to SeaKlear or our PROtech blend (chain stores carry Natural Chemistry to gain several sales of it before the issue is finally fixed as it contains phosphates itself...). You are absolutely correct, with all the science, technology, and years fertilizers have been around....wouldn't you think they'd have a chemical or "easy" fix for fertilizer / nitrates? One would have thought so, yet you still have to dump water and replace with fresh. to be honest, with the CYA at 93 and only 4 lbs. of chlorine/shock, it sounds like they are using the typical Dichlor which shouldn't be used as it is high in both CYA and pH. If anything, liquid Chlorine or Calcium Hypochlorite (no CYA or pH jump) should always be used to shock a pool into a desired FC level. Also, you were stating 50+ gallons of 6% bleach...that's household bleach. Isn't your local pool store selling 12-15% chlorine at a decent price in your area? I can't believe it's less costly to use a bleach half as concentrated to equal the same amount?
Here's the option:
lbridges thinks it's CYA (I think), I think it's Nitrates (like he said everyone has an opinion). It may be a good ideal to compare these two options.
1. 50+ gallons of household bleach (if that's the fix) would cost what? $50 on average?? Would it be more cost effective to dump that in the pool, IF it actually is CYA to match the corresponding levels then let both slide back to a normal level, taking a chance that this may not fix your issue.
2. Drain a good amount of water, then replacing with fresh, which will not only solve a possible CYA overdose, however solve the Nitrate problem if there is one at the same time. A little tip....if you call the city before filling your pool and tell them it's for filling your pool, they give you a huge discount on your water bill for the amount you tell them (not being wasted and no sewage fees).