Mustard Algae-help

[albacore45]

Hi I have lurking this forum for a few years, lots of good advice here. Heres my problem. I have had my in ground salt water, plaster pool for about 9 years now, very few problems. This winter I let it get away from me. My salt cell went bad, and before I knew it I had mustard algae. I cant seem to get rid of it. What really bothers me, is that is seems like its rooting into my plaster walls. I scrape it hard with an algae brush, but I still see big dull yellow stains in my carribean blue plaster. I have tried raising chlorine levels and I also use Orenda a phophate remover . It keeps coming back. Mabee I am not raising clorine levels enough. Please help with some advice, and a way to unstain my pool walls. I have a big 25Lb bucket of tricolor 99% powder recently bought to uses for shocking occasionally. Heres the specs on my pool.

21,000 gal inground gunite

PH 7.6
Free Cl 3-5
Alk 150
CY 100
45 PPM Borax

[BigDave]

You're right! You haven't been raising (or keeping) your chorine levels high enough. Not nearly high enough to battle mustard algae. Please see Ben's Best Guess Chart for reference.

I have a problem with the CYA level of 100ppm. 100ppm is the top reading of most CYA tests so your actual value could be higher. You can use the dilution method to verify: mix 1 part pool water and one part tap water (tap has no CYA), test the mix for CYA and multiply the result by 2.

How are you testing? We recommend the Taylor K-2006, you may want to consider the K-2006C, it has 2oz reagent bottles insted of 3/4oz, you'll use alot with the FC levels you're going to need to test. If you purchase through this link: Taylor Service Complete Pool Water Test Kit K-2006C, the PoolForum gets a commission to help keep the lights on.

The FAS-DPD test is the only way you'll be able to manage the process of cleaning your pool and the Taylor K-2006 is the only readily available kit that has it. Accept no substitutes!

[albacore45]

You're right! You haven't been raising (or keeping) your chorine levels high enough. Not nearly high enough to battle mustard algae. Please see Ben's Best Guess Chart for reference.

I have a problem with the CYA level of 100ppm. 100ppm is the top reading of most CYA tests so your actual value could be higher. You can use the dilution method to verify: mix 1 part pool water and one part tap water (tap has no CYA), test the mix for CYA and multiply the result by 2.

How are you testing? We recommend the Taylor K-2006, you may want to consider the K-2006C, it has 2oz reagent bottles insted of 3/4oz, you'll use alot with the FC levels you're going to need to test. If you purchase through this link: Taylor Service Complete Pool Water Test Kit K-2006C, the PoolForum gets a commission to help keep the lights on.

The FAS-DPD test is the only way you'll be able to manage the process of cleaning your pool and the Taylor K-2006 is the only readily available kit that has it. Accept no substitutes!

thanks for your help. If I were to use my granulated triclor 99% to bring my CL levels up high enough to kill it, how much in weight/volume should I add to a 21,000 gallon pool. i cant seem to find a calculator for the powder.

[BigDave]

OOPS! I missed that.
PLEASE don't do that. Trichlor will add 6ppm CYA for every 10ppm FC. Your CYA is already in the unknown / unmanageable area, we don't want to add more!

You didn't give us a Calcium Hardness number (important for a plaster pool), If it's low, you can chlorinate with Calcium Hypochlorite, if it's not, Bleach or Liquid Chlorine (same thing, different concentrations) is your only practical alternative (Litium Hypochlorite is an alternative but is very expensive).

How did you come by the numbers you gave us?

We really need to get a range for your CYA before we can figure out the FC level and dosage to super-shock your pool (and if that's really what you want to do).

Some wall marts carry the HTH 6-way test kit (Check Availability) It is compatible with the Taylor K-2006 (it's made by Taylor) and includes a CYA test. It also includes an OTO based chlorine test which can give us gross estimates of the very high chlorine levels you'll need to kill the mustard algae. Let us know if you can pick one up, if not, then do get a cheap OTO / Phenol Red kit - you'll need it. Also, Order the Taylor K-2006.

[albacore45]

OOPS! I missed that.
PLEASE don't do that. Trichlor will add 6ppm CYA for every 10ppm FC. Your CYA is already in the unknown / unmanageable area, we don't want to add more!

You didn't give us a Calcium Hardness number (important for a plaster pool), If it's low, you can chlorinate with Calcium Hypochlorite, if it's not, Bleach or Liquid Chlorine (same thing, different concentrations) is your only practical alternative (Litium Hypochlorite is an alternative but is very expensive).

How did you come by the numbers you gave us?

We really need to get a range for your CYA before we can figure out the FC level and dosage to super-shock your pool (and if that's really what you want to do).

Some wall marts carry the HTH 6-way test kit (Check Availability) It is compatible with the Taylor K-2006 (it's made by Taylor) and includes a CYA test. It also includes an OTO based chlorine test which can give us gross estimates of the very high chlorine levels you'll need to kill the mustard algae. Let us know if you can pick one up, if not, then do get a cheap OTO / Phenol Red kit - you'll need it. Also, Order the Taylor K-2006.

I had my water tested at Leslies. their analysis said 100 PPM CYA. I can get it down a bit over time by draining and filter backflushing. My calcium hardness is 200 PPM. I just did a complete water change this winter as my TDS had hit 700.

What i have is a pail of 99% pure triclor powder, it has no CYA added. I have a friend in the pool business, so I can get my chemicals direct from SCP at wholesale. So what I need to know is how to convert this powder to PPM in the pool water

[BigDave]

...99% pure triclor powder...

Trichlor is stabilized chlorine and has CYA in it when it's pure. Dichlor is also stabilized and yields 9ppm CYA for every 10ppm FC.

Leslie's CYA test also is unlikely to be able to tell 100ppm CYA from 200ppm CYA.

If your water's new, How did it get so much CYA in it?