Black Algae, High CH--drain or not to drain?

May 7, 2017
8
Houston, TX
#1
Hello,

I have a gunite pool with many black algae spots and some mustard algae. My CH is also at 550 causing some calcium scaling (it's not too bad). I tested my fill water, and it is at CH 200. I think my pool could greatly benefit from replacing some water. I am thinking because there is so much black algae in the pool and my CH is high, I could drain the pool, clean scaling and algae (while at it, pressure wash the moldy sidewalks around the pool), and then refill with CH 200 water. Here is my concern: I live in Houston, and am scared to think that my pool could pop when I drain my almost 10,000 gallons of water from the pool and the spa. Has any of you TFP'ers done this procedure in Houston successfully? Also, am I correct to think that getting rid of black algae once and for all would be much easier after I drain the pool? What are some techniques to do that and also remove calcium buildup?

Thank you,
Sergei
 

duraleigh

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Apr 1, 2007
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Sebring, Florida
#2
Welcome to the forum:wave:

You can't get rid of the black algae or mustard algae by draining.

Normally, the most compelling reason to drain is high CYA......what is yours?
 
OP
OP
S
May 7, 2017
8
Houston, TX
#3
Thanks for the reply, duraleigh.

I did not mean that I would get rid of algae by just draining the pool. I watched videos about chlorine washing the algae and acid washing (is it just for stains?). I don't know what other methods there are to get rid of black algae once the water is down, but I am thinking it would be more thorough cleaning than now (easier possibly?).

My CYA is super low--at around 25. I even put in a gallon of instant conditioner and nothing changed! It's really strange. But I am more concerned about my CH of 550, and black and mustard algae. I read here that when CH is high it is difficult to keep water chemistry in balance. Also, the water does not look as clear. Is 550 considered high enough to drain and refill?
 

Patrick_B

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LifeTime Supporter
Jun 7, 2011
14,999
Midland TX
#4
High CH can be a problem, but it doesn't make the water harder to balance. It's part of rhe overall balance, but CH 550 is nothing to worry about. Its only slightly high, but easy to manage. It makes pH more important to watch along with the TA, but focus on pH first. The pH is always something important to keep an eye on, just a little more so with your CH.

You dont need to drain, but some time spent in Pool School will help you. Please start there with the ABCs, some other basics, and then SLAM. You will need to elevate the free chlorine up fairly high, and keep it there for a good while. This is a shocking process we call SLAM.

This requires a certain type of test kit, so can you tell us which one you have?
 
OP
OP
S
May 7, 2017
8
Houston, TX
#5
OK. So from what I read, it should be enough to scrape the heads of black algae with the metal brush and keep FC at mustard algae shock level for a couple of days in order to get rid of black and mustard algae for good. Is that correct? No pressure washing, chlorine washing, or acid washing required for the same results?

I have K-1515-A for testing my chlorine levels.
 
OP
OP
S
May 7, 2017
8
Houston, TX
#6
After I scrape off the heads of black algae, how high should my FC level be? Pool Math Calculator shows between 6 and 8 as normal for my 45 CYA. Is that enough, or should FC be higher than 8? If yes, how high?