Mustard algae treatment with higher CYA (75)

[haz]

Hello all. So my pool developed mustard algae, I think after the chlorine level decreased when I left town and with the heat and water evaporation, the water level went below the skimmer and warped some of the pipes, making the pump lose prime and stop working. The mustard algae, which I had once previously in another pool, was dust/pollen-looking stuff at the bottom of the pool when you brush the bottom (and no pollen-producing plants nearby), and I could get pollen-looking stuff again if I brushed a few hours later. In case it's relevant, it's been very hot here in South Florida recently.


I have been doing BBB, by the way, so I don't know if any other types of chemicals were added, but the pool had notably low CYA and calcium when I got it.


I did an OCLT (overnight chlorine test), and it went down from 4 to 2.5 (Fas-Dpd Titrating test). Chemistry was as follows:
pH 7.8
TA 95
CYA 70-75 (now 65-75 with some added water)
CH 370
CC 0.5
Salt 3400


So I decided to SLAM with liquid chlorine, targeting 29 per pool math, first bringing pH down to 7.2 (TA went to 85). The next day, there was no notable mustard algae when brushing the pool. The water is (and was) clear. There are no ladders or things like that in the pool that could have algae trapped behind them, and I've taken all the lights out of their sockets. I opened and brushed the hole for the umbrella. I've opened the cleaner line and propped open its door to have SLAM-level chlorine flowing through. I cleaned the filter, which was clean-looking.

I have yet to get the suggested 1 point FC loss on the OCLT to proceed to mustard algae FC levels for 24 hours. I've been brushing and vacuuming daily, and I've left my robotic cleaner brushing and vacuuming the pool all day. FC results are as follows:
Day 1 night : 32
Day 2 morning: 29

Day 2 night : 34

Day 3 morning: 28.5

Day 3 night : 30

Day 4 morning: 27
Day 4 night : 30.5

Day 5 morning: 23.5

Day 5 night : 29.5

Day 6 morning: 24.5

Day 6 night : 29

Day 7 morning: 24.5

Day 7 night : 30.5

Day 8 morning: 26.5


For one thing, I check the chlorine levels around 7 AM. There is light out but no sunlight on the pool (at that hour the house shades the pool anyway). I assume the indirect light at that hour wouldn't yet cause any notable extra chlorine loss.
The second thing is - I failed to find any post discussing whether the "1 point FC loss rule" holds as the target FC level increases. My CYA is at most 75, which is around what is recommended on this forum for an SWG pool. But it's clear that the higher the FC, the more you lose - it's more a percentage of the FC level than an absolute FC loss. I started SLAMming for a FC loss of 1.5 in the presence of clear mustard algae, which was a 38% loss. Now i have 4-5 point FC loss nightly, which is around a 17% loss - much better percentage, but much higher absolute number. The mustard algae has not been visible, the pool is clear, and the CC is <1 since day 1, so it seems logical that what’s important is the % FC loss rather than an absolute number.

I would appreciate any thoughts on whether I should do something differently. Looking forward to hearing your thoughts. Thanks!

 

[needsajet]

I would definitely test CYA again to see where you're at with CYA now, after the dilution from adding water and also from the multiple days SLAMing.

Your test results suggest that you keep on SLAMing and brushing daily as well. Are you able to raise the chlorine several times per day?

Hope any other repairs are going OK, and sorry to hear about the dramas.

 

[haz]

I would definitely test CYA again to see where you're at with CYA now, after the dilution from adding water and also from the multiple days SLAMing.

Your test results suggest that you keep on SLAMing and brushing daily as well. Are you able to raise the chlorine several times per day?

Hope any other repairs are going OK, and sorry to hear about the dramas.

Thanks for the reply. I did retest CYA, and it's now around 65-75 (so I'm still targeting FC of 29 for CYA 75).
I was raising the chlorine several times per day with liquid chlorine at least during this last long weekend, so that by the evening reading, I was already at around 29-30 and didn't need to add anymore.

The pool equipment has been fixed, thankfully. In case anymore needs the name of a good pool fixing company (they don't do pool cleanings, just fix and install pool equipment) in SE Florida, PM me. My normal pool repair company, who were always excellent, couldn't come soon, and I was hoping to have it fixed quickly to avoid having to go and buy chlorine. I tried a place that had like a 4.8 rating from dozens of online reviews that was near me, and their receptionists were very nice, and their technician wanted to change all the pipes for around $600, plus he mentioned 2 lights should be replaced, so $800. I eventually had my usual tech come and he fixed it for a little over $200 and confirmed that my lights worked fine - they looked fine to me!

 

[needsajet]

a little over $200 and confirmed that my lights worked fine - they looked fine to me!

That's great to hear!

Yep, keep up the SLAM and don't give in until the overnight loss is minimal.

If there's no swimming happening, go up to the mustard algae level for 24 hours to knock that out. Extra brushing if you can fit it in.

You could try then letting the FC drop down to around 15 and doing an OCLT to see what happens.

 

[haz]

That's great to hear!

Yep, keep up the SLAM and don't give in until the overnight loss is minimal.

If there's no swimming happening, go up to the mustard algae level for 24 hours to knock that out. Extra brushing if you can fit it in.

You could try then letting the FC drop down to around 15 and doing an OCLT to see what happens.

We haven't been swimming - I was unclear as to whether there was any problem with swimming at FC levels that high so we just kept out of the pool.
So you think it would be OK if I now try going up to mustard algae levels now and see how it goes? I think years ago with another pool I had mustard algae right after adding CYA (so higher CYA) and also ended up in a similar situation and just went for it successfully.

 

[needsajet]

That's what I would try, yes.

It's safe to swim when:
pH 7.2 to 8.0
FC at or below SLAM level (40% of CYA, so at CYA 70 PPM, that's up to 28 ppm)
And you can clearly see the bottom of the pool at the deep end

 

[haz]

That's what I would try, yes.

It's safe to swim when:
pH 7.2 to 8.0
FC at or below SLAM level (40% of CYA, so at CYA 70 PPM, that's up to 28 ppm)
And you can clearly see the bottom of the pool at the deep end

Thank you for that guidance! I'll let you know how it goes after the mustard algae FC increase and OCLT at a lower FC level. Really appreciate the help.

 

[haz]

That's great to hear!

Yep, keep up the SLAM and don't give in until the overnight loss is minimal.

If there's no swimming happening, go up to the mustard algae level for 24 hours to knock that out. Extra brushing if you can fit it in.

You could try then letting the FC drop down to around 15 and doing an OCLT to see what happens.

So I did the mustard algae FC level for 24 hours and then stopped adding any chlorine - targeting 29.4 as my CYA is now 50. Here were my FC numbers:
last night, end of mustard levels: 30.5
night 24-hours later: 16.5
am: 14.5
night: 11
am: 11
night: 9
am: 9

So I've passed the OCLT (now 2 days straight) but only at lower FC levels. That was my thought - in 24 hours the chlorine dropped 14 points after mustard algae FC levels, 2 point FC drop from 16.5, but no more FC drop when down to 11 & 9. Also, the percentage drop over 24 hours decreased each day as the FC dropped (46%, 33%, 24%, 18%). Thanks again. Hopefully I don't need to do this again, but something to keep in mind if slamming with a high CYA and therefore high target FC.

 

[needsajet]

If it were mine, I'd keep FC up to 10% of CYA for a while, although it's not necessary, just peace of mind. I would add FC at 5ppm to raise it to 7ppm for a while, or set the SWCG to keep it around 5-7 ppm FC.

I would also avoid raising CYA for a week or two, but I'm very conservative. The TFPC level for your pool is 70-80 ppm CYA, but you will also be getting heaps of protection at 50 ppm CYA, so just a safe period in case anything surprising happens, but there's every chance that it won't. Have you done a CYA test lately?

Congratulations on finishing the SLAM!

 

[haz]

If it were mine, I'd keep FC up to 10% of CYA for a while, although it's not necessary, just peace of mind. I would add FC at 5ppm to raise it to 7ppm for a while, or set the SWCG to keep it around 5-7 ppm FC.

I would also avoid raising CYA for a week or two, but I'm very conservative. The TFPC level for your pool is 70-80 ppm CYA, but you will also be getting heaps of protection at 50 ppm CYA, so just a safe period in case anything surprising happens, but there's every chance that it won't. Have you done a CYA test lately?

Congratulations on finishing the SLAM!

Thank you! Great thought - waiting a little before increasing the CYA in case I need to slam again. Yes, I did CYA recently and it's at 50.

Wouldn't 11.5% of CYA (or around 10%, as you mention) as per:

Chlorine/CYA Chart

EDIT: You will find a simplified and standardized version of this chart at Pool School, Chlorine / CYA Chart. Chlorine/CYA Chart by Chemgeek FC = Free Chlorine in parts-per-million (ppm) CYA = Cyanuric Acid in parts-per-million (ppm) CYA ........... Min FC3 ..... Target FC ...... Yel/Mstrd...

www.troublefreepool.com

be a good target for the long term?

 

[needsajet]

Yes, certainly.

SWCG targets are a bit lower, but for now, if it were my pool, I'd keep it at the non-SWCG levels, just in case of a surprise. Either way is fine.

 

[haz]

Yes, certainly.

SWCG targets are a bit lower, but for now, if it were my pool, I'd keep it at the non-SWCG levels, just in case of a surprise. Either way is fine.

Sorry, yes I thought that chart looked too high. So minimum 4.5% of CYA for SWG, but I'll go w/ the 10% like you suggest for 2 weeks and then lower. What FC % would you target, maybe 6%? If I target the minimum, I could get in trouble when the chlorine demand goes up, before I realize it. Thanks again!

 

[needsajet]

The FC/CYA Levels is the best reference, for sure.

Some people, myself included, keep a jug of pool chlorinating liquid or 10% bleach on hand. Before a pool party, I add a quart, which looks after the extra FC demand.

 

[haz]

The FC/CYA Levels is the best reference, for sure.

Some people, myself included, keep a jug of pool chlorinating liquid or 10% bleach on hand. Before a pool party, I add a quart, which looks after the extra FC demand.

Good idea, again, thanks again for all of your help!