Algae Bloom and superchlorination

Algae problems in swimming pool water.
Green (cloudy) water or slimy pool walls.
Black algae. Mustard algae. Pink or white pool mold.
kaptn

Algae Bloom and superchlorination

Postby kaptn » Mon 21 Jun, 2010 07:55

My stats as of Friday morning from a pinpoint analysis. I was getting similiar reads from my Taylor kit on Chlorine and PH.

FC 0.7
TC 1.6
CC 0.9
TA 139
PH 7.2
CA 30
Copper 0
Iron 0

I kept gettting a low reading on the FC...around the 0.5 color and test Strips. I would throw in three bags of shock and check it later still no change. I was still getting Mustard Algae growing 1 day after vacuuming to waste. spent the weekend vacuuming a couple of times and putting in some shock.
Sunday I decided to shock the heck out of it and put in 8 bags of dilluted dichlor shock (this is what the pool calculator recommended 6 bags). checked my FC about 30 min after and it showed a lot of chlorine (my kit only goes to 5ppm so it was way above that). Woke up this morning to check the FC and it still shows a high FC reading. The TC is equivalent in the color as the FC. My question is when do you lower the FC down and how do you do it? I still have about 8 bags of shock...should I dose it again when I get home if my FC still shows a high reading?


chem geek
Pool Industry Leader
Pool Industry Leader
Posts: 2382
Joined: Thu 21 Jun, 2007 21:27
Location: San Rafael, California

Algae Bloom and superchlorination

Postby chem geek » Mon 21 Jun, 2010 12:41

The FC will drop on its own if the pool is exposed to sunlight -- in direct sun it should drop by up to half or a little more if your CYA level is truly 30 ppm. Only use more Dichlor if you want your CYA level to get higher -- probably 50 ppm would be OK AFTER you get rid of any algae but then maintain a minimum FC level at least 7.5% of the CYA level so around 4 ppm FC if you have 50 ppm CYA.

Don't forget the chemical rules of fact that are independent of concentration of product and of pool size:

For every 10 ppm Free Chlorine (FC) added by Trichlor, it also increases Cyanuric Acid (CYA) by 6 ppm.
For every 10 ppm FC added by Dichlor, it also increases CYA by 9 ppm.
For every 10 ppm FC added by Cal-Hypo, it also increases Calcium Hardness (CH) by at least 7 ppm.

So Dichlor raises CYA a lot so be careful about how much you use. When your CYA level is where you want, then use chlorinating liquid or 6% unscented bleach as your primary source of chlorine, but you will need to add it every day or two unless you have a partially opaque (such as blue) pool cover.

Read Defeating Algae and note that for yellow/mustard algae you need a higher shock level of 60% of the CYA level, so that's around 18 ppm FC with your current 30 ppm CYA. Be sure to get behind light niches and under removable ladders since this algae likes to grow in shady areas. Also put in all poles, toys and other equipment that will get into the pool later so that you kill the algae and do not reintroduce it into the pool.
kaptn

Algae Bloom and superchlorination

Postby kaptn » Mon 21 Jun, 2010 16:25

OK...so if the shock CYA ppm is correct then I would presume since I used 8 lbs of dichlor that this should jump my FC up to about 30ppm which would make my CYA rise from 30ppm to about 57ppm.

I will have it tested tomorrow.
chem geek
Pool Industry Leader
Pool Industry Leader
Posts: 2382
Joined: Thu 21 Jun, 2007 21:27
Location: San Rafael, California

Algae Bloom and superchlorination

Postby chem geek » Mon 21 Jun, 2010 21:04

Please get your own good test kit -- either the Taylor K-2006 or the TF-100 because pool stores are notorious at doing the testing incorrectly, especially for the CYA test.
kaptn

Algae Bloom and superchlorination

Postby kaptn » Tue 22 Jun, 2010 07:18

well tested last night at 8:30 when I got off work.....pump ran all day.

FC...0.5
PH...7.2

threw in 5 lbs of dichlor shock shut pump off after 1/2 hour for the evening. Tested again this morning and still holds fine over the night (no sun obviously)

FC....way past 5.0 (5 lbs of 18,000 according to the pool calculator would be 22.0)
PH....7.2
ALk....90

not sure what the CYA is but brought in a sample to be tested this morning. Why would I have a high FC and then get home later in the day and it to be completely gone. I can see if it went down to 2-5 range but completely gone (test strips backed up this reading as well).

I am getting fustrated as Hockey Sticks!!!
kaptn

Algae Bloom and superchlorination

Postby kaptn » Tue 22 Jun, 2010 12:00

Ok just got back from being tested....these numbers were as of this morning at 7:00am

FC 10.0
TC 10.0
CC 0.0
TA 106
PH 7.1
CA 143 (yikes...higher than what I thought)
CH 172

no iron nor copper

saturation -.040

Looks like I am going to have to do some draining of water to lower CYA down. I get the feeling when I get home that my FC will read about 0.5 again.

Pool Store Suggestions:

1. add 5 lbs oc calcium hardness...(nope not doing that til I get a chlorine reading)
2. Change Return eyelets to point in one direction and downward to increase circulation at the bottom of the pool more....(interesting thought)
3. 1 qt of Mustard Fighting Algaecide (Strike Out is what he called it).
4. Brush Pool.

I have been vacuuming instead of brushing the pool...would using a brush be more effective against the algae???

Return to “Pool Algae & Green Pool Water”

Who is online at the Pool Help Forum

Users browsing this forum: No registered users and 1 guest