Mystery stain/algae - help needed

[Bearcatkeith]

Ok, I started off with brown/black stains/algae in the bottom of my vinyl liner. I initially rubbed a chlorine tab across the stains and no effect. I rubbed a vitamin c tab across the stains and it seemed to remove part of the stain. So, I decided it was a metal stain and brought FC to 0 and PH to 7.2. Then treated with 5 lbs of AA (25,000 gallon pool). The result was that none of the stain was removed.

I thought maybe my vitamin c tablet test somehow did not give me an accurate result and I then changed my thinking to be that maybe it was a copper stain. The reason being that my gas heater started the season off with a cracked heat exchanger so I decided it must have leaked some copper into the water.

So at that point I decided I would at least get my pool back to normal levels and worry about the stains later. So I shocked it and added chlorine tabs to the skimmer baskets. I did this in the evening and by the next morning my stains were completely gone! Now, I have changed my thinking back to being some sort of organic covering on the bottom of my pool. Today is 1.5 days after shocking the pool and now I see part of the stain/algae returning (maybe 10-25% of the original stain has come back in the exact same spots).

Additional info is that I have never been able to rub any of the stain off of the liner. I have tried brushing and scratching it with a fingernail. I cannot get any to come off on a fingernail so I am still very reluctant to think it is algae.

Any idea what my issue is?

Thanks,
Keith

 

[kcindc]

Welcome to TFP! You've come to the right place. There are a few things we need to know to give you good advice.

First, please update your signature, in the upper right click "settings", then on the lower left select edit signature. Please add the details of your pool and equipment.

Second, how are you testing your water? If you have your own test kit, please tell us the test kit name.

Third, we need a complete set of test results, FC, CC, PH, TA, CH and CYA.

Karen

 

[Butterfly]

 

[Bearcatkeith]

Ok, here we go. Sorry for delay.

FC 17 (keeping high because I suspect mustard algae - using liquid bleach)
CC .5
TC 17.5
PH 7.2
T/A 70
CH 200
CYA 70

I recently shocked at a high level and stains/algae completely disappeared. I am convinced to keep the FC high and hopefully it will kill off the suspected mustard algae. Any thoughts?

 

[jblizzle]

Please add your location (City, State or City, Country) to your profile as described HERE as it will help us help you in the future.

You FC is not even close to high. See the FC/CYA Chart. With a CYA of 70ppm, you need to maintain a FC level of 28ppm just for the normal ShockLevelAndMAINTAIN Process.

 

[Bearcatkeith]

Before I waste water (getting CYA lower) and liquid chlorine can someone tell me that mustard algae cannot be scraped off with even a fingernail? I cannot get any of it to come off no matter what I do physically. The only thing that makes it disappear is a lot of chlorine. Am I just bleaching a stain? All other types of algae I was always able to scrap some off one way or another.

 

[jblizzle]

Sounds like an organic stain and not live algae.

 

[Bearcatkeith]

Any ideas how to best get rid of the organic stain?

 

[kcindc]

Chlorine. Unfortunately your CYA is too high. High levels of CYA protects the chlorine from doing its job. Chlorine is what is needed for organic stains, but your high CYA is keeping it from doing its job.

Regardless of the source of the organic stain (black or muster or leaf stains), you need high levels of chlorine with brushing to get rid of it. Until you drain to get your CYA levels down, you won't be able to make much progress on the stain.

As stated earlier, with your CYA that high, you should be shooting for a FC of 28... otherwise you won't be able to make any progress.