Large dark stain on bottom in deep end.

heyjude53

Member
Jun 17, 2024
7
Northern, indiana
Pool Size
27000
Surface
Vinyl
Chlorine
Liquid Chlorine
Located in Northwest , Indiana. Pool is an in ground, vinyl liner with and emerald shape with sloping deep end sides. Measures 36 x 24 with an estimated 25,000-26,000 gallons of water. I use a sand filter and a 1.5HP hayward pump. I have an automatic chlorinator for the 3"try-chlor tabs. ( I was trying to stay away from use of the chlorinator, as my CYA climbed quite high last summer.
I had huge difficulties getting water balanced and clear, but my chemistry seems to be within parameters. I have ordered the Taylor 2006 kit, but in the mean time measure my own pH and alkalinity, and then use a test strip. I just took a water sample to the pool store which uses a computer analysis. Results FC 2.12, pH 7.6, alk 136, CYA 42, hardness 160 and phosphates 978.
My water is clear but I have a large dark stain that comes and goes on liner in the deep end. The liner is 9 years old and we also had an exceptionally warm winter, with several days in the 70's throughout March and April. The stain has disappeared when I have super chlorinated and/or used an algaecide only to come back. I have also used 3 applications of Revive which helped clear the pool initially and also to have lowered phosphates from 1200 ppm. Following TFP I have put in 152 oz of 12% chlorine in everyday, only to have it used up in 24 hours. Water temp is 85 and air is 95. I do vacuum every other day, and have been backwashing every 4-6 days.

I am seeking advice about the stain, but also about alkalinity and use of alternating between tabs and liquid chlorine.
According to TFP is that my alkalinity is high. I have muriatic acid but I am a little uncomfortable using it, and I also have pH down. What would be the best advice on how to lower it.

Also curious as if I can keep the CYA in an ideal range of 30-40 (or even up to 100) why tabs are so bad. Does anyone else out there alternate between the two forms of sanitation or is that just not a good idea, and if not , why not?
Thank you
 
I suggest you do nothing except add your normal doses of chlorine to your pool until you get your test kit.

When you get your test kit post your results and we can discuss. We don't trust pool store tests to give advice based on it.

When you get your test kit do a Overnight Chlorine Loss Test. If you fail the OCLT then you need to follow the SLAM Process

Once you have your test kit and pool algae free we can discuss alternative means of chlorination.



 
I received my test kit. Here are the results testing in the morning. I will say that free chlorine went from 5 to 3 over the prior evening (as clearly seen on a test strip-I know not the TFP method-but pretty clear).
FC 3.6
CC.2
pH 7.4
Alk 12
Hardness 230
CYA 33
Temp 83

My water is clear and has been clear although as soon as the chlorine levels drop to 3ish the stain on the bottom comes back. I also have evidence of perhaps algae on the seams on the liner. SO is the next step SLAMMING until I get less than 1 ppm charge overnight for FC? Or do I do something different because my water is and has been clear for 4 weeks. Or is SLAMMING part of the process so I eventually don't need to be putting gallons of chlorine in day and night.
When I SLAM, I assume not good to put the solar cover on overnight?
I also have 25 lbs of chlorine tabs on hand and would like to work those into the equation-plus it would help raise my CYA over time.
Thank you
 
How did you measure TA at 12? Not likely to have that result with a pH of 7.4

Round up CYA levels to next decade number.
 
Just want to follow up. I started SLAM process on Sunday and after testing two to three times a day, adding gallons of chlorine, the pool finally passed all criteria on Wednesday morning. I redid the overnight test again on Thursday morning and it passed again. The dark stain on the bottom, which drew me to this site is also gone!! Not sure if I had algae growing in the 9 year old liner, as it is worn from chemicals dropping to the bottom because it wasn't anything that I could vacuum away, but as of this time it is gone and the water is sparkling blue. Thank you!!!
My CYA is still below 40, but I am rounding up it is 40. So the final question (maybe) would it be ok to use chlorine tabs for a limited use until I use up 25 pounds that I have which might take me into next summer. What would be your recommendation for limited use.
Again, thank you for your guidance. I am sold on this site.
 
You can use Tabs, but you must always follow this...Link-->FC/CYA Levels

SLAM, and maintaining FC for your CYA starts to become difficult when CYA is above 60. When you are above 60 CYA, the only way to reduce CYA is to replace water.

If you want to use the tabs, use them until CYA gets to 60, then switch to liquid chlorine, Menards is the best source for you.

CYA degrades over time. When CYA lowers to 40-50, then use tabs until CYA gets back to 60 and start using liquid again.
 

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