The fight is almost over... or so I think.

I'm helping my friend/old boss rehabilitate a pool that hasn't been used in 5+ years - the landlord neglected it badly. A month or 2 ago, he and a friend began dumping in trichlor shock and quat algaecide from the Depot to attack the low chlorine and at least kill some of the algae. A few weeks ago, I've been dumping in trichlor shock on a daily basis and at least several doses(2 doses of HTH quat over 2 days, 2 bottles of polyquat over 3 days) and this weekend we used up the trichlor and started using HTH cal hypo instead. Now the water is sparkling clear, except for the black algae on the sides that is now slowly but surely fading away with daily brushing. It'll take at least a week of shocking, IMO.

I'm telling him to start on the BBB method to save on chemical costs, or to use cal hypo tablets to maintain Cl levels and bleach to tweak the levels. He doesn't have a good test kit, but I'm going to pick up one that also has reagents for CH and CYA. I'm also debating either to use bleach, cal hypo skimmer tablets, or a combo of both.

What should I do at this point? The biggest problem here is consistency and sticking to schedule - they're busy parents and they run a business as well. I'm tempted to use HTH skimmer tabs out of convenience but I think the BBB method is cheaper. The pool is a 17,000 concrete/plaster pool. At last check, free/total Cl was .5/2 before shocking and 5+/5+ afterwards. pH was at 7.2, TA was at 120.

We really are going to need cya and calcium hardness numbers before we can advise what is the best chlorination method to use. Also, what type and size is the pool. You are a good friend to help them. Repost with those numbers (and also current other readings as well as by then these that you posted will no longer be current) and we'll be glad to help. Welcome to the forum!

Yea, I'll be back today or tomorrow with a better test kit - a 6 way test kit to measure CYA and CH numbers and I got more shock as well as skimmer tablets, just in case.

Just taken a few moments ago:
Cl: 5 ppm using HTH OTO reagent (which looks like the Taylor bottles)
pH: 7.2
TA: 110 ppm
CH: 350 ppm
CYA: 60 ppm

I'm thinking it's a good time to tweak the CH levels, but the CYA could come down a little bit - the owner and I used trichlor until I enlightened myself. Earlier this week we dumped in 2 lbs of trichlor shock along with Green to Clean which I think is responisble for the CYA.

/edit - I didn't test the CH right - I retested it and while the instructions on the test kit say the water should turn red when there's hardness, it was actually purple-red. I then added the titrate until it turned visibly blue, which was 35 drops.

You definitely don't want to use trichlor tabs or any more dichlor to shock--you don't need your CYA levels coming up any higher than that for now. My understanding is that ideal CH for plaster pool is 200-400, so I think you're right on the money where you are. If it were my pool, I'd go with bleach, or even better, liquid chlorine if you have it available to you (it's the same as bleach but 10% concentration and sold in bulk). With a CYA of 60 it will take a good bit of bleach at the beginning to get to your base target, but the upside is that it will last longer so you probably won't have to add it everyday. You're going to have to maintain your Cl no lower than 5, and up to 10. It will take a few days of testing morning and night to see what your Cl consumption is, but I'm betting that you only will have to add every 2nd or maybe even every 3rd day, if you maintain it on the higher end of that range.

Janet

I have pool bleach readily available from the hardware stores, Home Depot, Wal-Mart, and the pool store - Home Depot being the cheapest and ironically, Wal-Mart and the pool shop being the most expensive.

Right now, I got 1 HTH skimmer tab steeping in the skimmer and added 1.5 lbs of HTH shock in the pool last night. There's a little trichlor still in the pool but I'll yank those today. I'll also retest as well today.

/edit - except for CYA which jumped up 10ppm, everything seems the same - but I need a DPD test kit to figure out FC and Cl consumption.