Mustard Algae, 2nd year of battle

Ok. I've decided to go ahead and post, even though I know the answer is probably here somewhere. This is such a great forum and has been so helpful to me in the past. However, I'm going to be hosting a couple of important events this summer (one child's wedding in July and another in August!) and it is going to be important that my pool looks and performs perfectly.

Last summer I battled mustard algae all summer long. I have lugged endless bottles of bleach, vacuumed, brushed, added filter socks, tested (I have one of the good Taylor test kits) and still at the end of the season last year I had the mustard brown silty-looking stuff on the bottom of my pool. I really want to get rid of it this summer. Otherwise my pool is so beautiful, clear sparkly water.

I'm wondering now if my algae problem is being caused by my high ph/TA. I didn't worry about it last summer because the pool is vinyl, and I never noticed any scaling.

Yesterday, I decided I was going to kill that algae if it didn't kill me first. Since the pool is still a bit too cold for comfortable swimming, about 76 degrees, now was the time. Bleached vinyl liner or no bleached vinyl liner.

I put 16 1.5 gallon bottles of 5/6 % bleach from Wally world into the pool. The FC level was high enough that the test in my kit didn't turn pink even with 2 scoops of the R-0870, so was probably over 50.

Here are my numbers this morning.

FC 30
CC .5
pH over 8.0, very pink
Acit demand 9 drops to 7.4
TA is 180
CH is 220
CYA is 40

Now, I have been using only bleach since last summer with one exception. During the winter, which was exceptionally mild here in our part of TX, whenever the water temp would get above 55 degrees or so I would add a powdered shock, Dupont Multifunctional Shock (Sodium dicloro-s-triazinetrione) just to make my life easier and have more time for quilting. I'm getting kinda old to be lugging all those bottles of bleach around, but of course I can't find anyone around who is willing to maintain my pool using only the chemicals I say. They always try to sell me something I don't want.

So, I know I probably have algae because of the drop of FC in my pool from last night till this morning. I will do this process again this evening, until the FC stops dropping. But, and here is my real question, is the high pH affecting this process? Exactly what is bad about a high pH if you have a vinyl pool? Our water is incredibly hard, and always will be. Does this high pH mean that I will always battle this algae?

Wow, I hope that you still have some color left on your liner!!

I'll let Ben, Richard, or some of the other chemists address the effectiveness of the high pH, but just wanted to say that you can't trust your pH readings with your chlorine levels that high. Even with the better kits, the pH will read falsely high when the chlorine levels are as high as yours are.

The dichlor that you used is fine--it has a low pH, and will tend to drop the pH in your pool, but you just have to be careful to watch your CYA levels because it is stabilized and they will rise.

Actually I can't tell that it faded my liner a bit. The pool looks beautiful this morning, nice and blue. Still that little bit of pesky brownish silt that will need to be vacuumed out today.

Wow. I lost 15 ppm over the day. I guess the algae is still dying. I can hear them crying from my back porch!

I just put 10 more 1.5 gal bottles of bleach into the pool, and I vacuumed it again today. I must say it sure looks beautiful and inviting. It is starting to really sparkle. So, question still is, do I add muriatic acid, to try to bring the pH down?

You don't know what your pH actually is because you can't get an accurate reading when the chlorine is that high.

Ok, just tested FC for the night and it is 45. Even in the moonlight I can see the drain at the deep end. Cool. Will run all tests again first thing in the morning.

Just a suggestion for when you get the current batch killed and your FC is back to normal, you might want to consider adding 50 ppm borate to your water for it's algaestatic action and it is effective at keeping mustard algae at bay since you have had problems with it in the past. It will last you all season if not longer and you only need to worry about raising the borate level when it drops to 30 ppm. It is easy to test with LaMotte Borate test strips. It's easy to add using only borax and muriatic acid. You will need 15.5 boxes of borax (76 oz.) and between 4.25 to 4.5 gallons of muriatic acid. to bring a 20k gal. pool to 50 ppm so it is actually often less expensive in the long run than using polyquat and lots of chlorine to combat outbreaks.
With the pump running broadcast 8 boxes of borax into the pool and then add 2 gallons of acid. Brush the pool to mix everything. (Brushing down the sides of the pool all around is most effective.) Add the rest of the borax and 2 1/4 more gallons of acid and brush again. Let the pool cfor 24 to 48 hours and make final adjustments to your pH.
Since your TA is so high you might want to consider lowering it first since it is going to be easier to do BEFORE the borate addition since the borate acts as a secondary pH buffer but it can be done either way. I would not worry about the TA unless you had problems with keeping your pH in line. You did not make it clear if your pH was always high or just reading high during the high chlorine levels you are keeping now to kill the mustard algae. If your pH was constantly climbing and you had to add a lot of acid to keep it in line it might be easier to just bite the bullet and lower the TA at the start of the season and then add borate.

Very interesting about the borate, Waterbear, thanks. I just ran my numbers again, here is the evening results:

FC 22
CC .5
pH 7.8
TA 180
CH 240
CYA 35

This morning I ran the FC test but did not have time to post before I had to leave for work, but it was 40, which is an improvement over the night before. BTW, my pool temp is 78 and outside temp is now 74. It was well into the 80's today here, bright sunshine. Should I add more CYA?

And yes, I have had problems keeping pH lowered. pH bounce pretty much describes my pool, if it means bouncing UP.

Ok. So for tonight, I'm adding the last two bottles (1.5 gal) bleach that I have, which according to how my pool has reacted in the past should raise my FC level to just over 30. I am also going to add 2 lbs of the Dupont Multifunctional Shock (Sodium dicloro-s-triazinetrione) that I have, just to make sure my FC for the night remains high, and I figure my CYA could be a wee bit higher. Borate treatment will have to wait till next week. Son's future in-laws are coming Sunday (!) to discuss wedding, and they'll be seeing our house for the first time. Bleah. I'm already starting to hate this.

So far I'm seeing you post chlorine results from each night, but none from first thing in the morning so that you can tell how much chlorine you're actually losing to the algae. Some of the chlorine you're losing when testing at night only is being lost to the sun during the daytime, but the way to tell just how much the algae is consuming would be to test at night and again first thing in the morning, and then compare the two.

Janet

For yellow/mustard algae, it likes to grow in shady areas so check under any removable ladders (if the pool were a plaster pool, then I'd have you check behind light niches, but I assume with your vinyl pool that you don't have those). If you don't kill it at its source, it'll come back unless you keep the chlorine at a higher level (around 15% of the CYA level for maintenance; shock level is 60% of the CYA level) which can be impractical as it is more costly.

chem geek, I do have a pool light, but it has never worked since we bought the house. Well, I'm assuming it doesn't work, since I can't figure out how to turn it on. No switch that I can find seems to work it. So, I probably do need to clean behind it.

Mustard algae is back. I still have not done the borax thing, but hope to be able to do it this week.