MUstard algae keeps coming back!

tmartini27

Member
Jul 27, 2018
16
DALLAS, TX
Hi All,

I'm new to this group but have been stalking the site for awhile now. Every summer it seems for the past 2-3 years we deal with mustard alge once it gets super hot. We live in Texas and have a shallow pool so the water temp heats up quickly despite the 2 shades we have hanging above. Oddly, the algae doesn't grow in the shady areas. I'm pretty sure it's algae as there are yellowish brown spots mainly on the walls of the pool and the water gets cloudy. We have a 15k gal IG plaster pool that has been here since before we bought the house 10 years ago. Prior to 2 weeks ago we were using chlorine pucks and powder shock to maintain our pool. Our pump runs 10-12 hours a day and we have a cleaner that runs 2 hours a day. From my research it looks like our CYA is likely the problem. I bought a Taylor FAS-DPD K-2006 kit 2 weeks ago and have been testing daily. My most current results are:

FC - 10
CC - 0
PH - 7.8
TA - 110
Ca - 300
CYA - 100. The pool store tested it and said it was 80. The CYA numbers are from 2 weeks ago.

I switched to bleach about 2 weeks ago and have been keeping my target FC at 11. The lowest it dipped was 8, most days it's 9.5-10 before adding chlorine. Do I need to keep the FC higher to prevent it from coming back? Is it necessary to drain the pool to fix the CYA before the algae will go away for good or can we shock it? We were hoping we'd lose enough with splash out as we have kids that are constantly in and out of the pool. After the last shock, we bleached all the toys and floats that go in the pool and washed all the suits in the washer. I'm at a loss and would greatly appreciate any advice! Thanks!

Teresa
Dallas, TX
 

tim5055

Mod Squad
TFP Expert
LifeTime Supporter
May 11, 2014
11,040
Franklin, NC
Welcome to the TFP pool! :splash:


100 is the limit of the CYA test, so you have to do a diluted test. While the full instructions are in the Pool School, here is the short version. Mix 50% pool water with 50% tap water. Use this mixed sample as your test water. If still at a 100 you will need to dilute more. The problem is that when doing a diluted test not only do you multiply the rage of the test you multiply the error rate of the test, so results are a ballpark - not an absolute. Here is a great chart by JamesW to explain dilution rates and what you multiply the results by to get an approximation of your CYA level.

Pool water......Tap or distilled water.........Multiply result by

....1...................1................................2
....1...................2................................3
....1...................4................................5

Splash out is not going to reduce sky high CYA. You will need to do a drain and refill of a good bit of water.
 

tmartini27

Member
Jul 27, 2018
16
DALLAS, TX
Ok. I diluted and CYA came back at 110. How much of a drain are we talking about? Thanks!

Welcome to the TFP pool! :splash:


100 is the limit of the CYA test, so you have to do a diluted test. While the full instructions are in the Pool School, here is the short version. Mix 50% pool water with 50% tap water. Use this mixed sample as your test water. If still at a 100 you will need to dilute more. The problem is that when doing a diluted test not only do you multiply the rage of the test you multiply the error rate of the test, so results are a ballpark - not an absolute. Here is a great chart by JamesW to explain dilution rates and what you multiply the results by to get an approximation of your CYA level.

Pool water......Tap or distilled water.........Multiply result by

....1...................1................................2
....1...................2................................3
....1...................4................................5

Splash out is not going to reduce sky high CYA. You will need to do a drain and refill of a good bit of water.
 

jay_mcc2

Bronze Supporter
Jul 1, 2018
36
Friendswood, TX
Have you found the Poo Math calculator. It’s got great functions to help with figuring out your chemicals.

https://www.troublefreepool.com/calc.html

According to the calculator you need to drain over 60% of the pool to get your CYA levels down to 40.

Also do add your pool features to your signature so that other more knowledgeable folks can help you out faster. Do you have a SWG? CYA levels are recommended a little differently for those that do.

http://www.troublefreepool.com/content/128-chlorine-cya-chart-slam-shock

Yes, the only way to get rid of CYA is by replacing your pool water.
 

tim5055

Mod Squad
TFP Expert
LifeTime Supporter
May 11, 2014
11,040
Franklin, NC
Ok. I diluted and CYA came back at 110. How much of a drain are we talking about? Thanks!
There is no 110 on the CYA tube. Don't equate “just a little over 100” to a number, the tube is not marked for such extrapolation.

At this point I would recommend at least a 33% water exchange to get the CYA down before more testing. For vinyl lined pools leave at least one foot of water in the shallow end to keep from floating the liner and all pool owners are cautioned that in areas with a high water table lowering the water too much can “float” the pool out of the ground.

It would help if you edit your signature and add the following information so we can better frame our answers to you.


  • List what test kit you use to test your water
  • The size of your pool in gallons
  • If your pool is an AG (above ground) or IG (in ground)
  • If it's IG, tell us if it's vinyl, plaster/pebble, or fiberglass
  • The type filter you have (sand, DE, cartridge)
  • If you know, tell us the make and model of your pump and filter.
  • List any other equipment you have: SWG, second pump, etc.
  • Please mention if you fill the pool from a well or are currently on water restrictions

Information in your signature will show up each time you post and it makes advice more accurate as we know what equipment we are dealing with.
 

tmartini27

Member
Jul 27, 2018
16
DALLAS, TX
The 110 came from a diluted test with 50% pool water and 50% tap water. We drained the pool this morning down to the jets. We don't have a submersible pump so were at the mercy of the main drain. I'm estimating we were able to drain at least a 3rd of the pool. In the process of refilling now. Couple questions - how long after refilling the pool do we need to run the filter before testing? I'm thinking I've read 6 hours but wanted to double check. Also, when we slam, do we need to be concerned about cleaning all the toys and floats that go in the pool? I've read that algae can sneak back in the pool that way but am thinking as long as the chlorine is high enough, it should kill it. Is this correct? And lastly, is there a right way for the jets to be positioned to support proper circulation? And I updated my signature. Thanks for all your help!
 

tim5055

Mod Squad
TFP Expert
LifeTime Supporter
May 11, 2014
11,040
Franklin, NC
The 110 came from a diluted test with 50% pool water and 50% tap water.
But, the tube is based on a logarithmic scale (not linear) so other than at the marks you can't guess what something is. Right now all we know is that you are north of 200.

how long after refilling the pool do we need to run the filter before testing? I'm thinking I've read 6 hours but wanted to double check.
You are just looking to mix the water well, so a few hours with good circulation should be fine.

Also, when we slam, do we need to be concerned about cleaning all the toys and floats that go in the pool? I've read that algae can sneak back in the pool that way but am thinking as long as the chlorine is high enough, it should kill it. Is this correct?
Generally you really don't need to worry about the floats/toys, but at teh end of your SLAM Process (after you have passed the 3 criteria) you can toss them in and "clean" them with the high chlorine level.

And lastly, is there a right way for the jets to be positioned to support proper circulation? And I updated my signature. Thanks for all your help!
You are just looking for the water to "flow" to all areas of the pool and mix the water well.

And I updated my signature.
Looks good!


Now, I'm afraid you may be in for more drain/refill cycles.
 

tmartini27

Member
Jul 27, 2018
16
DALLAS, TX
Great! Sorry, i wasn't clear on the CYA. When is used 50/50 my level came back at 55 so i multipled by 2 to get 110. So hopefully with the drain, we'll be close to an acceptable level. Thanks for your help!
 

tim5055

Mod Squad
TFP Expert
LifeTime Supporter
May 11, 2014
11,040
Franklin, NC
Great! Sorry, i wasn't clear on the CYA. When is used 50/50 my level came back at 55 so i multipled by 2 to get 110. So hopefully with the drain, we'll be close to an acceptable level. Thanks for your help!
Ah, that makes me feel better. But, again - consider your CYA 120, alwasy round up. Half way between 50 and 60 on the tube is not 55.