Pool / Spa Issues - Skin rashes, mustard algae

[CarlD]

I have two problems:
1) Your FC is 'way too low given your CYA levels. You need to have your FC ALWAYS between 5 and 10ppm, and you need to shock it 20ppm, regardless of your CC. You MUST raise your FC
2) Your CH is EXTREMELY high. 400ppm is as high as it should go, and, with a tile, concrete or similar pool, should be above 200. With a vinyl pool CH can go as low as 0. You are likely to get milky water and possible scaling.

[robertrael]

Thank you CarlD, I appreciate the quick response you gave me. I have yet to shock my pool as I am out of supplies. I have approximately a 13k gallon IG pool and want to shock to the 20ppm with the pool currently at about 5ppm. Is it possible to estimate how many bottles of bleach I should buy from say my local Walmart (8.25% Sodium Hypochlorite)? I will of course buy more to have on hand for keeping the chlorine at the correct level, but I do not have my Taylor book with me (which might tell me how much I need).

Thanks.

[CarlD]

Sure. A quick rule of thumb is that one gallon of 8.25% will add 8.25ppm of FC to a 10,000 gallon pool. It will add only 4.125ppm to a 20,000 gallon pool, or 16.5ppm to a 5,000 gallon pool. Adjust accordingly!

[robertrael]

Thanks again for all of your help. I've successfully shocked my pool to 20 ppm. So now, when the chlorine comes down to normal levels, 5-10 ppm, everything should be good, with the exception of the CH? I don't know what to do about that, we're coming into our worst drought ever, so I'm not sure about being able to get away with draining the pool even part way (1/3rd? 1/2)? I will continue to look into solutions for that one.

[CarlD]

I think the short-term solution is to drop your Total Alkalinity to around 60-80, maybe lower. If you pH doesn't start constantly trending down, it's OK. It MAY slow down scaling and milky water.

Check your fill water's CH.

[robertrael]

Well here I am again. Let me start out by saying the advice provided here was invaluable. I've kept the pool nice and clear for just over a year. I had some circumstances that prevented me from taking care of the pool for about 3 weeks and now I am paying the price for it. I have a chlorine tablet feeder which allows me to place 3" di-chlor tablets in there. I also use liquid chlorine. This combination allows me to keep the pH just perfect pretty much. Very rarely do I need to add Muriatic Acid or Soda Ash/Baking soda. During those 3 weeks, I didn't run the pool pump much, which would have supplemented some of the chlorine via the feeder. I like to leave the pool covers on to save on water evaporation and chemical detoriation (whatever it's called), but to get a hold of this problem I have left it uncovered for about 3 days now.

If you don't have time to read all that, here is the summary:

Tested this evening:

7 PPM FC (Brought it up to 20 PPM estimated on Sunday)
Just about no CC
7.4 pH
125 TA
500 CH - drought is now worse than when I complained about it last year, so not sure about draining
30 to 48 CYA (I could still see the dot or imagine the dot at 30, but the night before with house lighting, I lost the dot at 48ppm CYA)

Pool and spa are about 18,000 gallons total. Spa looks damn near clear through all this.

I added 2.5 one gallon bottles of 8.25% sodium chloride to the pool, which I estimate to raise the FC to 19ppm, but for some reason now that calculation seems wrong. I will check the FC in about 30 minutes to see what it's at. Chances are it's hit 20ppm and a little beyond (from past experience.)

So when I uncovered the pool there was a lot of algae growth. We brushed the heck out of the sides and ran the pool pump a lot. Now the pool is a cloudy teal color. Would you say I am on the right track to fixing my issue?

[SunnyOptimism]

Well here I am again. Let me start out by saying the advice provided here was invaluable. I've kept the pool nice and clear for just over a year. I had some circumstances that prevented me from taking care of the pool for about 3 weeks and now I am paying the price for it. I have a chlorine tablet feeder which allows me to place 3" di-chlor tablets in there. I also use liquid chlorine. This combination allows me to keep the pH just perfect pretty much. Very rarely do I need to add Muriatic Acid or Soda Ash/Baking soda. During those 3 weeks, I didn't run the pool pump much, which would have supplemented some of the chlorine via the feeder. I like to leave the pool covers on to save on water evaporation and chemical detoriation (whatever it's called), but to get a hold of this problem I have left it uncovered for about 3 days now.

If you don't have time to read all that, here is the summary:

Tested this evening:

7 PPM FC (Brought it up to 20 PPM estimated on Sunday)
Just about no CC
7.4 pH
125 TA
500 CH - drought is now worse than when I complained about it last year, so not sure about draining
30 to 48 CYA (I could still see the dot or imagine the dot at 30, but the night before with house lighting, I lost the dot at 48ppm CYA)

Pool and spa are about 18,000 gallons total. Spa looks damn near clear through all this.

I added 2.5 one gallon bottles of 8.25% sodium chloride to the pool, which I estimate to raise the FC to 19ppm, but for some reason now that calculation seems wrong. I will check the FC in about 30 minutes to see what it's at. Chances are it's hit 20ppm and a little beyond (from past experience.)

So when I uncovered the pool there was a lot of algae growth. We brushed the heck out of the sides and ran the pool pump a lot. Now the pool is a cloudy teal color. Would you say I am on the right track to fixing my issue?

You need to perform what some call a SLAM procedure - Shock, Level and Maintain.

1. SHOCK

You need to raise your pool's FC level to shock level. However, you have reported black algae which could be mustard algae. Mustard algae is VERY difficult to get rid of as it is a type of algae that forms in clusters with a thick bio-film surrounding it. It's that adherent and protective bio-film that keeps the algae fixed to your pool surfaces AND protects the algae from chlorine. Mustard algae typically requires FC levels that are roughly 60% of your CYA level. Therefore, if you assume a 50ppm CYA, then your mustard algae shock level of FC is 30ppm. That sounds really high, and it is. Mustard algae is extremely difficult to kill.

Also, if you have a plaster pool, you might need to invest in a steel wire pool brush as opposed to the nylon type. Mustard algae requires lots of scrubbing to dislodge it from the pool surface and to break apart the algae clusters and filaments so as to better expose the algae to chlorine.

2. LEVEL

As alluded to above, FC level must match the extent of the problem. Assuming you have mustard algae, you MUST use the higher chlorine levels or else you will not kill it.

3. MAINTAIN

This is the crucial step. You MUST MAINTAIN the mustard algae shock level and not allow the FC to drop below it during the duration of the procedure. This means testing your water every two hours and adjusting the FC with bleach as needed. In the beginning, this process will be daunting as the high chlorine levels will get used up very rapidly as it kills algae and oxidizes organics. It will seem like, the minute your pour the bleach in, it gets used up and it is! But maintaining the shock level is absolutely critical.

Also, during this time, your filter is going to get plugged up with lots of dead algae and organics. You must keep a eye on your filter pressure and backwash/clean your filter regularly if the filter pressure rises more than 20% of the clean pressure.

So how do you know when you're done? Three criterion -

1. Your overnight chlorine loss (OCL) as measured from sunset to sunrise is less than 1ppm. All pumps must be running 24/7 and you should shut off the salt water chlorine generator if you have one.

2. Your CC's are less than 0.5ppm

3. Your water is crystal clear with no visible signs of algae anywhere in the pool.

ALL THREE CRITERION MUST BE MET.

Once you pass the three checks, you hold your pool water at shock level for an additional 24hours and then let it drift down to normal.

During the SLAM procedure it is a good idea to throw any pool toys you have in the water so they get cleaned as well. You should remove any metal objects from the water (such as removable stairs) and, if you have a light niche, you can remove the light from it and let it float in the pool to expose the interior of the niche to the high FC. Algae can hide in lots of places including the piping system so it is critical to run all pumps and water features during the process so your entire system sees the high FC.