algicide

[brook]

Here is some background info:
I bought my house last May and became a pool owner for the first time. The day I moved in, I called a man who does pool maintenance to come over and give be some training on my pool.
He deducted that the previous owner used tricolor as a sanitizer exclusively. My PH was well below 7 and there was no chlorine at all. Other than a small area of green algae under the pool ladder, the water looked good.
He serviced the pool and his instructions were to shock the pool with cal-hypo 65% when the color on my test kit registered 1.5, and he estimated that to be about 2 weeks. I tested about 3-4 times a week, and about 6 weeks later my chlorine was still over 3. I decided to go ahead and add shock anyway because the floor of the pool had some slippery areas.
Finally in the late summer/early fall I determined that my CYA levels were very high. They were well over 100. I quit using trichlor as a stabilizer in late Sept. and did not use any all winter or this last spring.

Currently the only problem I am having is with mustard algae. It appears for a few days immediately after I add shock. However, it is always present on the steps in the shallow end.

Is this thriving or dead mustard algae?

Because of my high CYA, I would need to use a ridiculous amount of chlorine to kill it. So instead, on Monday I used Bioguard MSA algicide with copper, and then shocked again immediately after adding the algicide (that is what the pool store folks told me to do).

My questions concern the correct usage of the algicide. I don’t know if it killed the mustard algae or not. Today (Wednesday), I went to the pool store to ask if I need to add more algicide, and was fortunate enough to speak to one of the pool maintenance guys instead of the usual high school kids at the counter, and he said “don’t use anymore algicide, it is dead”.
I don’t know if I should accept it as true or not.
Any ideas?

My readings before adding shock on Monday were:

FC 4.5
CC 0
PH 7.2
TA 90
CYA 100
CH 200


Thanks, Brook


25,000 gal in ground , vinyl, cal –hypo 65%, trichlor, polaris.

 

[JasonLion]

You would be much better off if you could bring the CYA level down by replacing some of the water. One of the problems with high CYA levels is that the common test reads levels higher than 100 as 100, so it is difficult to know your true level.

With CYA at 100 you need to maintain FC levels around 8 to 13 and never below 8.

You can find out if the algae is dead or not by measuring your FC level in the evening and again first thing in the morning. If the level remains the same overnight then there isn't anything growing in the water.

Mustard algae tends to grow on the walls on the shady side of the pool. Yellow/orange dust that floats around near the bottom and tends to accumulate in drifts is almost always pollen or dead algae. If you really have mustard algae it will be very difficult to get rid of with CYA that high.

It sounds like you tend to run with the FC level too low for your CYA level and so get low levels of algae almost all the time. When you shock the algae will die and accumulate on the bottom.

 

[JohnT]

Algaecide is primarily a preventative, and doesn't have a great deal of effect on existing algae. Copper algaecide is a particularly poor choice if someone who swims in your pool is blond. Copper is what causes green hair. You aren't going to see algae appear immediately after you shock. You might be seeing dead algae on the floor, or it could be iron in the water reacting with the shock.

There is no need to routinely shock if you maintain consistent proper chlorination. Following poolstore "conventional wisdom" won't do the job. What you really need to do is to do a partial drain and refill to lower your CYA. In the meantime, you should maintain your chlorine at or above 7.5ppm due to your high CYA level.

 

[brook]

Jason and John, thanks for the info. I know a partial drain and refill would be the best solution. I live in Atlanta and we are having a severe water shortage, so I was trying to avoid that for as long as possible.
My main reason for believing it is mustard algae is that when I brush it off it comes back in the same place a few hours later.
Also, I asked the pool store people if I could buy something to take the metal/copper out of the pool that I put in with the algicide, and he said that I would be required to show them a water sample with a FC of 1-2 or they could not sell it to me.
I don't know anything about metal removes at all.
Does that sound right?

 

[ivyleager]

We've been in drought conditions here in North Carolina for as long as Atlanta, so I feel for you. I am one pool owner who has lived through high CYA +100. Yes, I did have to keep 8ppm FC in the pool, which was challenging. Because of human fallability, I routinely added poly60 algicide 2x month at the mainentance level. I also made sure that I had the filtration running pretty near +12/day that summer. I switched to bleach, and I survived the high CYA level. I did not have a visible algae bloom that sumer, but I did get "slippery" vinyl once or twice. Then I just shocked and turned up the circulation for a day or two. By the next season opening, my CYA had "plunged" down to 70.

It can be done. There is hope.

CaryB

 

[brook]

Ivyleager.
What kind, and how much bleach did you put in ?
Did you ever drain any of your water? Brook

 

[JasonLion]

A sequestrant will bind to any metals in the water and prevent them from causing problems, but nothing I know of other than water replacement will actually remove metals from the water. And what any of that has to do with proving low FC levels is beyond me.

"when I brush it off it comes back in the same place a few hours later" doesn't really prove anything. Each pool will have a place where the water circulation slows down a little and things tend to settle. Fine dust and dead algae will both tend to settle out there. If it is adhering to vertical surfaces it is mustard algae, but if it is settling on the bottom then it probably isn't (though it is difficult to be sure either way).

 

[ivyleager]

Ivyleager.
What kind, and how much bleach did you put in ?
Did you ever drain any of your water? Brook

I used the bleach calculator to determine how much to put in. With my high CYA level, I was able to hold the chlorine for about 36 hours, so I'd add every other day. It was probably like a 2 large bleach jugs at a time.

I have NEVER drained any of my water. Last season I suffered through a low CYA level of 35.....I was adding a ton of bleach daily. I actually like my pool to be around 60-70 CYA ppm.

CaryB

 

[brook]

Jason, your imput makes me feel better, and that maybe it's really not mustard algae. It's never on the walls. It's mostly on the steps and in the shallow end on bottom.