Algae on vinyl liner, but clear water

[Squirlz00m]

I'm new here. 20x40 pool. DE filter, liquid chlorine only. Always have crystal clear water but have had black spots on my vinyl liner for several seasons that I want to get rid of. They do not budge with brushing. I can scrape them off with a credit card but I can't swim down deep enough to get them out of the deep end. I have a hunch that algae formed on some type of calcium deposit. We have very hard water. I just purchased a TF-100 test kit because I was thinking I would need to SLAM to get rid of this. My CYA level seems to be non-existent. So I'm thinking I need a stabilizer? Guess I'm just looking for advice or reassurance that I am on the right path?

 

[Texas Splash]

Welcome to TFP! Well, let's not get too far ahead of ourselves until you get the test kit. That will tell a lot. Until that time, you might try scarping some of that off and wiping on a paper towel. See if it meets the Black Algae criteria from the link below. Continue to add chlorine only for now. We'll know more once you post some test results of your own.

Black Algae

This guide provides a step by step procedure for eliminating black algae in your concrete or gunite pool. Read full post here.

www.troublefreepool.com

 

[Squirlz00m]

Here is a piece scraped off and smeared on a white paper.

 

[Squirlz00m]

Also I have my test kit. What should I test?

 

[Texas Splash]

What should I test?

FC
CC
CYA
PH
TA
CH

 

[Squirlz00m]

FC
CC
CYA
PH
TA
CH

FC = 0
Cc=0
CYA= less than 20
PH= 8.2+
TA=110
CH=325

 

[Texas Splash]

Those numbers need some help ASAP. So let's get busy with the following:
1. Use a sock to pre-soak and add another 10 ppm of CYA. After about 30 min, squeeze all the mushy stabilizer out of the sock.
2. Use muriatic acid to lower the pH down close to 7.2.
3. Use liquid chlorine to increase the FC to 12. The FC of 12 would be your SLAM FC level.

It will be interesting to see how that substance reacts to the SLAM FC level. Regardless, start the SLAM as soon as you can after doing steps 1 & 2 above. Even though the water may seem clear, look can be deceiving. At some point you will do an Overnight Chlorine Loss Test which is an excellent gauge to see if algae is still brewing in the water.

There are 3 criteria to passing the SLAM Process. Once you've met those criteria let's readdress those things you scraped to see if they are getting any better.

 

[Squirlz00m]

Those numbers need some help ASAP. So let's get busy with the following:
1. Use a sock to pre-soak and add another 10 ppm of CYA. After about 30 min, squeeze all the mushy stabilizer out of the sock.
2. Use muriatic acid to lower the pH down close to 7.2.
3. Use liquid chlorine to increase the FC to 12. The FC of 12 would be your SLAM FC level.

It will be interesting to see how that substance reacts to the SLAM FC level. Regardless, start the SLAM as soon as you can after doing steps 1 & 2 above. Even though the water may seem clear, look can be deceiving. At some point you will do an Overnight Chlorine Loss Test which is an excellent gauge to see if algae is still brewing in the water.

There are 3 criteria to passing the SLAM Process. Once you've met those criteria let's readdress those things you scraped to see if they are getting any better.

I added a gallon of muriatic acid and 2 lbs of stabilizer about 24 hours ago. My new results:
FC =2
CC= .5
CYA =less than 20
PH = 7.2 or 7.5
TA= 90
CH = 325

 

[Texas Splash]

For the CYA, did you use the sock method to add stabilizer? Pre-soaked in a sock then squeezed out completely?

I would add about 5 ppm worth of liquid chlorine. Your FC needs to be somewhere in the range of 4-5 right now.

 

[Squirlz00m]

Yes I put the stabilizer in a sock in the skimmer for about 15 minutes and then dumped it out in the skimmer. I just added 2 more lbs but haven't dumped it. It is still in the sock.

 

[reggiehammond]

Tie the sock to a broom stick or pool pole and hang in the pool. Reason we don't want it in skimmer is that if it's not fully dissolved, it will just cake up in your filter and take longer to make its way into the pool water.