Mustard Algae - Won't go away even with high FC levels

[Windcrest]

Hi everyone,

I am a new pool owner with what appears to be reasonably balanced pool water but I still get Algae sticking to the side. When I brush it, it comes off easily and you can see the green/brownish algae swirl in the vortex of the brush. I over added Chlorine when I first got the house and it has been stable for the last month around 7ppm so there hasn't been spikes or dips in the amount of FC.

FC 7
TAC 7
CH 210
CYA 90
TA 100
pH 7.4
Copper 0
Iron 0
PHO 1000

Before I dump a hundred dollars worth of chemistry to try and get everything under control (Shock, Algaecide, Pho remover etc) I wanted to see if anyone has any opinions. The filters are fiber filters that run at 14psi when clean and get changed when pressure increases to 26-28. It is typically taking about 7 days for the filter pressure to rise and is shorter if I am more diligent about brushing the sides (I do it every couple days).

Thanks for any info or suggestions anyone has.

 

[tim5055]

Welcome to TFP!

It sounds like the pool store is planning on using your bank account to fund their retirement program. Ignore all the things you are talking about.

You need two things
1. Your own accurate test kit
2. Lots of liquid chlorine

With pool store testing the numbers are usually wrong, especially the CYA

You need to do some reading in Pool School, starting with Tne ABCs of Pool Water Chemistry and the SLAM process.

 

[Richard320]

Welcome!

Ditto on the test kit. I wouldn't trust pool store numbers. What you want is a FAS-DPD test kit. You can get a Taylor K-2296 or a TF100. Pool School - Test Kits Compared

Let's say your pool store is one of the rare good ones that does accurate testing. If your CYA level is 90, mustard shock level is <gasp> 49 To get your pool from 7 to 49 just once will take 14 gallons of Clorox. It will take even more than that to keep it up there until the Mustard Algae is gone. It's cheaper to drain and refill!

If by chance, you get your own kit and the CYA is actually at a more reasonable number, then you perform the SLAM process and then jack the chlorine higher to finish off the mustard algae.

Pool School - SLAM - Shock Level And Maintain
Pool School - Mustard Algae

If the terms are confusing, start with Pool School - ABCs of Pool Water Chemistry and if you've been using dry forms of chlorine, read Pool School - How to Chlorinate Your Pool

It's normal to feel the first few weeks here. Once you get a test kit and start doing, it will all make sense.

 

[Windcrest]

I spent a lot of time reading the Pool School articles and didn't fully appreciate the interaction between CYA and chlorine effectiveness. All of the information is very useful and I can see where following the process can minimize the spend on chemistry as all the "extra's" add up quickly. Draining the pool to get CYA down will only cost me about $50 to dispose of and replace 15,000 gallons of water so that is cheaper then continuing to pay for a lot of shock chemicals as it was costing $25/treatment for me.

Obviously there is an advantage to pulling out as much water as you can before you refill the pool so that you get the highest concentration of CYA out of the pool. Using the Pool Calculator it confirmed that I need to pull the water down to 55% in order to get the CYA back down to 40. I am curious if I can pull this down all at once (gunite pool) or if I need to only pull out a little at a time.

 

[tim5055]

As Richard pointed out, I would not trust pool store numbers - you need your own test kit. The pool,stores told me my CYA was about 90 and when I got my kit it was well over 200.

As to draining, the main threats to a gunite pool are the plaster baking/overheating in the sun and the pool floating out of the ground if you have a high water table.

 

[Windcrest]

I ordered the TF100 pool test kit today and it should arrive by the end of next week. I'm pretty confident the CYA is high so I am in the process of draining the pool now. My plan is to let out 1/3 of the pool water and then refill. I'll recheck the chemistry at the pool store and see how the numbers compared to the baseline reading to give me an indication of effectiveness before my new kit comes in the mail. Once I get that I will test myself and then look to repeat the drain and refill process.

 

[Windcrest]

I drained out and replaced 55% of my pool water. I received my TF100 test kit and tested the CYA at 70 now. My guess is that my CYA was well over 100 before as I expected the CYA to come down lower then 70. I am debating whether or not to pull additional water out of the pool to get the CYA down to 40ish or whether I begin the SLAM now with the current level.

For the mustard shock when is the best time to raise the FC to mustard shock levels. Is it best to SLAM for a day and then raise it up so it can drift back down or is it best to start at the mustard shock level and maintain that for a day. I suspect it is best to do in the middle of the SLAM.

Thanks for everyone's help!

 

[tim5055]

I drained out and replaced 55% of my pool water. I received my TF100 test kit and tested the CYA at 70 now. My guess is that my CYA was well over 100 before as I expected the CYA to come down lower then 70. I am debating whether or not to pull additional water out of the pool to get the CYA down to 40ish or whether I begin the SLAM now with the current level.

For the mustard shock when is the best time to raise the FC to mustard shock levels. Is it best to SLAM for a day and then raise it up so it can drift back down or is it best to start at the mustard shock level and maintain that for a day. I suspect it is best to do in the middle of the SLAM.

Thanks for everyone's help!

For mustard algae, you shock at the mustard level for 24 hours at the end of a normal SLAM

Pool School - SLAM - Shock Level And Maintain

Pool School - Mustard Algae

 

[Windcrest]

Looks like I got the water in balance and shocked the pool. The chlorine is maintaining at shock levels and I suspect it will remain there for a while as the temperatures are dropping so Algae growth will slow. The pool is the cleanest and easiest to maintain since I moved in!

Thanks for all the help and education!