First Post Needing Some Help with Mustard Algae

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Aug 8, 2013
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First of all hello everyone and thank you for all the information that is available on this forum. I am a relative beginner but learned a lot just from a little research. This may be a little long but I appreciate any help you can give me. A little background first. My family owns a RV Park and Cabins in Pigeon Forge, TN. We have been here 23 years and 12 years ago my dad installed a new 18,000 gallon in ground pool with what I call stucco sides but I'm sure it's called another term. The pool uses chlorine and has a sand filter. A couple years ago we started having problems with mustard algae growing when it rains or got really humid outside. We would scratch and carry on and nothing ever stopped it. We finally went to the company who built the pool and they recommended yellow out. We bought some and would shock it normally every week but it never really helped. It keeps coming back. This year we have finally had enough of spending money on this stuff because it has effectively quit working. I looked up on here what to do and first things first I purchased a tf-100 test kit. Here is my readings:
Chlorine: 5
Ph: 7.8
Bromine: 10
Total Alkalinity: 180
Calcium Hardness: 200
CYA: 110
Based on these results I believe I have determined that our chlorine number is too low relative to our CYA causing our shock not to work and the algae to grow. Does this sound correct before I spend more time and effort on solving this problem? Keep in mind this pool is heavily used in direct sunlight in normally a very humid east Tn. Also, we have neglected our sand and probably need to change it out to fresh sand. Any suggestions to our problem as well as suggestions to keep our numbers normal?
Thank you very much everybody.
Caleb
 
:wave: Welcome to TFP!!!

Are those results using the TF-100? If so, looks like you failed to do the all important FAS-DPD chlorine test.

I think you are close to grasping this. The CYA level determines the minium FC required to prevent algae, it also determine the shock FC level required when performing the SLAM process: pool-school/chlorine_cya_chart_shock
We do not "shock" a pool on a schedule. If you maintain adequate FC, then you will not get algae. We only SLAM when there is a problem ... like you have.

Sand never goes bad, but you should do a cleaning once a year as described here: my-sand-is-channeled-how-to-fix-it-t7626.html#p60821

The CYA maxes out at 100ppm, so you are likely well over that. The first step is to replace water to lower the CYA into the recommended range (30-50ppm). Then you need to SLAM. [slam:1svv8zzl][/slam:1svv8zzl]
 
First, I would do a diluted CYA test with 50% pool water and 50% tap water and double the reading to see if it is higher than 110. If it is, you will have to replace some water to get the CYA down. It will be almost impossible to SLAM with a CYA of over 100. For a CYA of 110, shock level is 26 ppm, and mustard algae level is 59 ppm. If you haven't already, read up in pool school, especially the article on SLAM, the ABC's of pool water chemistry, and the article on mustard algae.
 
jblizzle said:
JohnN said:
For a CYA of 110, shock level is 26 ppm, .
Click to expand...

Or shock level is around 40ppm if you follow the more agressive chart in Pool School.

Either way ... that is a lot of bleach and a lot of drops of reagent to test that high.
Click to expand...
Didn't realize there was that big of a difference between the pool calculator and the chart. I knew there was some difference, but I thought it was at most maybe 10 ppm. I'll be looking at the chart from now on.
 
Ok that's what I was looking for. Our cya was too high causing the amount of chlorine we used to not be enough which basically rendered our shock useless. Makes sense. So I need to lower the CYA level. And I will review those articles again as well. I will also try the 50/50 test in the morning when we do the daily cleaning. I keep reading about a FAS-DPD test but yet to see what it actually is. The laminated paper In the kit said nothing about it (which I guess is why I neglected to do it). Is there a article on that I can read up on and I will perform that as well in the morning?
I do not want you all to get a bad impression about our pool since I know commercial pools have a reputation. We clean/test every day and always have clear water with no "chlorine smell" people complain about, it's just we get some algae in it we scrub every day and I want it taken care of instead of throwing a band-aid on it. We got a business to take care of and last thing we want is customers seeing yellow on walls. Normally isn't bad but lately with the rain and humidity its gotten worse which got me to researching.
Thanks so much guys!
 
The laminated card in the kit ONLY discusses the FAS-DPD chlorine test. The OTO chlorine test is the yellow one with the pH test.

The FAS-DPD uses R-0870 powder and the R-0871 drops to change the water back to clear, that count determines the FC. Then add R-0003 if it turns pink, use R-0871 to turn clear again, that count determines CC.

More info about the tests:
extended-test-kit-directions-t25081.html
 

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Ok guys this morning I re-did the CYA test with 50/50 pool and tap water and received a reading of 80. The sun was to my back as well cause i specifically remembered noticing the sun changed the tint the other day. I also performed the FAS-DPD test and here are my readings- Free Chlorine: 24 drops X 0.5= 12, Combined Chlorine: 0 (water remained clear), Total Chlorine: 12. With those readings what does everybody suggest for us to do? Keep in mind I understand one way to reduce CYA is to drain pool water but based on the 50/50 test I would need to drain over half the water. That does not seem feasible for us to do two or three times a year. Thanks again everybody!
 
What type of chlorine do you use? Liquid chlorine is what we recommend as it does not add any extra chemicals to the water such as trichlor and dichlor do. Trichlor and dichlor add CYA to the water. If you use liquid then there will not be a need to drain the pool due to CYA.

If you want to clear up the algae and not have it return you must lower the CYA to 50 and then follow the SLAM process. If you follow our guidelines then you will not have to shock the pool and the algae will stay away for good.

If you can not SLAM now due to the pool needing to be used, you might be able to replace water a little at a time. Backwash the filter more often and longer. Start using liquid chlorine if you are not using it now so the CYA will not rise any more. When you get the chance to SLAM do it as this method will get rid of the algae once and for all.
 
Correct the CYA with 50/50 mix was 80. We use a chlorinator with chlorine sticks for lack of a better term. We buy them in a 50 pound bucket. As far as type of chlorine I'm not exactly sure but I can find out later. We can slam the pool any evening we wish because we close it at night. The main issue I am having is the CYA. The slamming process makes perfect sense to me and we have done that several times but in a little different way but next time we will switch. Why does CYA increase that much? What I am getting at is if we spend 300 dollars and do a partial drain and refill what is to keep CYA from coming back up? But I will try to backwash more for starters.
I am missing something cause we have not always had this problem until a couple years ago.
 
For every 10 ppm of chlorine you add from trichlor (the sticks) it will raise the CYA by 6 ppm. When you drain, you keep the CYA from rising by not adding any solid forms of chlorine. If you only use liquid chlorine or bleach, your CYA won't increase. The SLAM won't be able to be done in one night. It is a process, which usually takes at least a week, from what I understand.
 
If they are sticks, they are trichlor. From what you wrote, you are not following the SLAM process if you are only elevating the FC at night once. The SLAM process is only needed when there is a problem and it usually takes at least a few days to weeks.

Trichlor adds FC and CYA, the FC is consumed, the CYA builds up as you are seeing. As the CYA rises, the required FC to prevent algae from starting also rises. If the sticks are not adding enough FC, then the pool goes green. If you do not want the CYA to keep building up, you MUST stop using trichlor or dichlor and switch to liquid chlorine.

All of this is covered in Pool School.
 
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