Need some advice on partial drain for algae/CYA problem

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K

kingofterrors

Member
May 4, 2020
7
Belton, TX
Hello great people of TFP! I've been lurking around here since I put up my pool in August of last year, but I've been lazy and using pucks and cal-hypo. After opening 4-6 weeks ago, the water was clear and I just needed to shock and go on with using the pucks and cal-hypo.
A few days ago, the water turned slightly green and cloudy. I tested with my basic kit and there was no chlorine. The days have been getting much hotter, so I'm going to have to step up and test/adjust daily. I added the last 2 lbs I had of cal-hypo, then the next day started adding some 10% liquid chlorine and took the pucks out. I also have a fountain going for aeration in hopes that it will help. Today, there is still a lot of green on the bottom, but it's not very cloudy at all. I just got my 2006c test kit in last night and have been reading as much as possible. My test results are below. From what I can tell, I'm going to need to do a partial drain to get the CYA down and then adjust my PH and follow the SLAM procedure.
The only thing I can't find a real clean answer on is... Can you give me an idea of how much water I should drain? For everything else, it will change after the refill, and I'll just have to test again. I learned my lesson and will stop using the pucks and cal-hypo until I fully understand their place. :) Any advice would be greatly appreciated.
One more question is about the CH test. I add drops until it turns blue... It always looks purple to me. It started turning "purple" at 30. I added 10 more and it never changed from purple to blue. Is it just my eyes? Should I stop at "purple"?

Test 6/12/2020
(FC) Free Chlorine - 3.6
(CC) Combined Chlorine - 0.4
PH - 7.9
(CYA) Cyanuric Acid - 100
(TA) Total Alkalinity - 120
(CH) Calcium Hardness - 300

I'm new, so go easy on me. Hopefully my signature shows up...
 
You don’t really need to worry about CH in your vinyl pool. For CYA, one you follow the instructions about and have a better idea of what your actual CYA is, you’ll want to get It down to about 50 or even less to make your SLAM easier to do. In TX. Usually it’s easiest to SLAM with CYA around 30, but that’s a lot of water for you to have to replace.

Tagging @mknauss to advise you how to safely drain to a manageable CYA level.
 
I completed a slam last week. My CYA was 50, and after draining it ended up at 20. Only then did I find out ideal CYA level for slamming is 30. Had to add dry stabilizer to raise to CYA 30.

I agree you should get CYA down to at least 50. If you want to go even lower to 30, you need to drain 70% of your water.
 
Welcome to the forum!
With an aboveground pool you can drain down to leaving about half of the water depth in the pool. So you may have to do a drain and refill a couple times. So start looking for where you will put that amount of water, how you will drain it (siphon, pump, etc), and how you will fill it. This will take some time.
I suggest you read ABC's of Pool Water Chemistry.
 
Tested CYA again, this time using the dilution instructions, and came to a result of 90 after several tests. w/out dilution it looks like about 85-90 so I guess that works out fairly well. Not sure how I got 100 before, I only did the test once, so maybe I did something wrong. So, a target of 40 CYA, 1- (40/90) = 56%. I'll drain about half the water, fill it up again and see what I've got.
 
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Just a quick update, someone please correct me if I'm off track. Test results after filling are below. According to the CYA/FC chart for SLAM, I need to be at 16 FC. Using the pool calculator, it says I should add 2.3 gallons of 10% chlorine. I went ahead and added 2.5, since that's what I had. I'll keep the pump running and keep testing and adding chlorine a couple times a day as needed. I'll also try to do some reading tomorrow. :)

FC: 1
CC: 0.5
PH: 7.6
CYA: 42.5
TA: 140
 
How did you test a CYA of 42.5?? The test does not have that resolution. Round up to 50.

SLAM level FC is 20. Test your FC and sufficient chlorine to maintain that FC level as often as possible.
 
Keep your FC at 20 ppm by retesting and adding maybe 3-4 times daily for a day or two and then back off to two or more times daily until you complete the SLAM.

CYA is VERY subjective so we always round UP......call your CYA 50 and that's close enough.

Watch your filter pressure and brush and backwash as needed.
 

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I tested multiple times and kept getting 40 or 45, so I averaged the 2. I'll go ahead and round up per your advice. It's a good thing, because I don't know what I did wrong, but I must have set the wrong jug size in the pool calculator or something. Now when I enter 20ppm for the goal from 1ppm, it says to add 1.4 gallons. I guess I accidentally went overboard adding 2.5 earlier. I actually expected it to take a lot more than that. I'll test again in a few hours and see where I am. I'll get the hang of this eventually. Thank you both for the quick responses!
fc.PNG
 
Sorry, it was at poolcalculator.com. I guess I saw it on another thread. All of the threads I'm reading are running together. I ran through it again and it gave me the same result as you, 3 gallons. I didn't have my pool size saved from the time before.
 
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