CYA 150, Should I replace water before closing?

[anshiren]

Hi All,

New pool owner here and thanks for this great site, which helped me a lot. I have a in ground non-swcg chlorine vinyl liner pool of about 67000 liters, and since the house was vacant for about 3 months before I moved in, no maintain during this time. Yet the water is pretty clear and blue, only some small residuals at the bottom which i vacuumed (but within a day or two, it came back i suspect it was algae)

1 week ago, for the first time I took the water to a pool store and the staff told me the CYA was too high without telling me the number, and told me to drain 2 feet of water by backwash. I did for about 1 feet and wanted ask for a second opinion and went for another store. The other store provide me the testing as below, where CYA was 150 but staff said it's fine since in their table ideal was 30-200, and only issue is TA and FC is too low; and asked me to buy something to raise TA (i bought some and then went to Costco bought 6 kg of baking soda trying to practice TFP method) and use what's the rest of my previous owner's triclor and shock:
CYA 151
TC:0.4
FC:0.4
PH: 7.3
Total Alkalinity 74
Adj. Total Alk:29
Cal. Hardness: 227

Unfortunately I followed the instruction to put 3 triclor and shocked it three days ago (now i learned it will further raise the CYA) but today i read the chart Pool School - Chlorine / CYA Chart which shows my pool should only have a CYA level of 30-50. Per pool calculator i need to drain about 60-80% of water to reach it. I understand this is the right way to do it. But since I will be on vacation for another month with no one at home and return in October. So I will either close it before i leave, or leave it with no maintain for a month and come back and close it. So my question is, should I replace the water and adjust all reading to ideal now before closing, or should I simply pour lots of bleach to make it reach about 14-20 FC for 150 CYA (although I know CYA 100+ is not reliable reading). Also, is it suggested for me to close at the end of August (still 25 C degree+), or leave it for a month putting lots of bleach/Triclor.

Thanks in advance.

 

[JVTrain]

Welcome to TFP!

First and foremost, pool store testing should not be relied upon. It's typically not accurate despite their fancy computerized testing systems with exaggerated precision. It's also inconvenient as you have to travel to the pool store and listen to their usually poor advice. Do yourself a tremendous favor and get your own test kit. In Canada, the K-2006 by Taylor is your best option for testing. It has all the tests you need to maintain your pool and is the most important investment you can make for your pool.

IF (BIG IF) their results are moderately accurate:
CYA is indeed extremely high. I would address that issue now before closing. Here's why. You should maintain water chemistry and circulation until the pool water is less than 60 F or ~15 Celsius. At that temperature, algae grows very slowly. Pools should not be closed until the temperature is solidly below that temperature or the pool could go green before winter even hits. In order to maintain clear water until then, 150 ppm CYA in not manageable. At a minimum I would drain until you have 1 foot of water in the shallow end (to prevent liner shift) and refill before winter. THis will likely get you to a CYA that's manageable. You can fully complete lowering the CYA in the spring with another partial drain if necessary.

TA is fine where it is. Raising your TA at this point will only increase your rate of possible pH rise. I would not raise your TA at all. 60-80 ppm is recommended and yours is ideal right now.

Trichlor usage will continue to raise your CYA if you use it.

Shock usage may also continue to raise your CYA if it is dichlor based. If it is cal-hypo type, then it will raise your CH. If it's cal-hypo, you can certainly use it as your CH is not that high and CH is fairly irrelevant in vinyl pool, unless it gets 350+.

Bleach or SWG are the best methods to maintain sanitiation levels and not raise other chemical levels you don't want to.

None of this advice matters if you don't get a proper test kit and get reliable results. When you do get a test kit, post your test results so you can get concrete advice, rather than advice based on suspect numbers.