Pool / Spa Issues - Skin rashes, mustard algae

[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.

[SunnyOptimism]

A few other points to make -

Testing -

During this cleanup, testing can become tedious. The easiest way I found to test during this shock procedure is to only test FC/CC and to use the 10mL sample size which translates into 0.5ppm/drop of chlorine titration reagent. Also, if you keep a good log of FC and CC, you should be able to see the trend easily and then you can dose regularly during the daytime without having to test each and every time. The critical times for testing are in the morning and evenings (1st test of the day and last test of the day) as those are the ones you use for measuring your overnight chlorine loss.

Reagents -

Shocking a pool can very quickly use up the DPD powder and chlorine titration reagents found in a K-2006 test kit. If you can, order more refills BEFORE your start. Another way to save on reagents would be to dilute your water sample in half with DISTILLED water and then multiply your results by 2. I would only do this for the less critical testing times during the day and not the tests for the OCL. When you dilute your sample, the +/-0.5ppm accuracy of the 10mL sample now becomes more like +/-1.0 ppm. So your tests is less accurate and not appropriate for OCL determination.

[SunnyOptimism]

I was reading you post a bit more closely and I see you have a tablet feeder. How long have you been using it? Do you do regular water draining and refill?

I ask because trichlor tablets add a lot of CYA (stabilizer) to your water over time and, without regular water exchanges, you can easily build up CYA in your water over 100ppm. If I were you, I would retest your CYA again but do dilution testing. Take a sample of pool water and dilute it 1:1 with DISTILLED water. Test your CYA and then multiply the results by 2. If you need further dilution, you can take 1 part pool water and add it to 3 parts distilled water, test CYA and multiply by 4.

The CYA test is tricky and it can be interfered with by high FC or pH out of normal ranges. It's also best to allow the water sample to come up to room temperature if the pool water is cold as the CYA test should be performed on water that is at least 68F-70F.

During a shocking procedure to remove algae, you need to get all of the tricolor tablets out of the feeder. The extra CYA is not helping you. Long term, I think you need to ditch the trichlor tablets and just use bleach in your pool as the stabilized chlorine products just cause more trouble then they are worth. But that's a conversation for another day.