Algae bloom while getting CYA down to manageable levels

4JawChuck

Well-known member
Jun 13, 2010
223
Winnipeg, Manitoba, Canada
You can read my initial post regarding my pool situation here;

http://www.troublefreepool.com/finally-took-possesion-of-new-house-and-cya-is-over-140-t24944.html

To make a long story short (thank god I am on holidays to handle this) I had an excellent opportunity to drain and refill the pool today...it poured nearly non-stop all day which sped things up a lot. I managed to get another 6 inches out of the pool today, between the rain and the hose I was impressed with my progress considering my CYA was over 180 a few days ago.

All was going well, managed to fix the water hose supply and replace the tubing to the water slide so it works properly...some nasty crud living in the nozzles and dirty slide rungs etc made it a whole day affair to get it looking like new. Nice to be able to slide and not get an atomic wedgie when you went down. :lol: In between downpours I got the kids out to test the slide and give me a verdict, they all agreed it was awesome and lots faster with a little lubrication!

Then one of the kids mentioned the water looked green... :shock:

Since I was backwashing and monitoring water levels and scrubbing diving boards and water slides I just never really looked at the water color, it was cloudy and overcast so I wasn't paying much attention. My morning levels were;

FC=10
TC=10
CC=0
PH=7.8
TA=100
CH=80
CYA=?

The man upstairs must have been watching out for me since he led me to the pool chemical section at Rona while I was picking up hose and I got some dry acid and a litre of Muriatic at the same time...figured I would try both since my morning PH levels were a little high.

Of course the algae bloom took me by surprise so I acted quickly and dumped in enough shock to bring the chlorine up to 50ppm, I took a water sample prior to dumping it in so I could test the CYA now that my drain and refill was done for the day! Luckily I think I caught it in time, the water was cloudy and greenish until the chlorine took effect and the dry acid and muriatic got pressed into service to bring the pH under control...sheesh I'm supposed to be on holidays!

At this time the pool is clear and blue and the krawler is sucking up dead algae off the bottom after I brushed the entire pool well, my pre shock CYA levels were not bad compared to what it was...it is 100 now so my 50 ppm shock load was a good guess even if it was a little high. I didn't want to take any chances with my previous CYA readings being so high

Needless to say I think I am going to keep the pool in shock until I get the CYA to a normal level, adding water and dumping makes it hard to keep control of the pool chemistry...the rain wasn't my friend after all since I think it was the source of my algae. In hindsight I should have just got the water truck in to do a complete refill all at once and avoid all this drama and chemical wastage, it may be more expensive but my nerves are frazzled.

I'm just thanking god he pointed me to that acid shelf and I picked some up, adding the acid instantly cleared the pool of the cloudiness and precipitated the algae literally as I stood there watching...that PH is really important to make the shock process work! Thank god for this forum and all those that give out advice because I was checking here frequently to find answers from previous posts. :goodjob:

Thanks folks for all you do! :-D
 

zea3

Mod Squad
TFP Expert
LifeTime Supporter
Jul 10, 2009
11,094
Houston, Texas
Draining and refilling also reduced your FC, and rainwater washes dirt and other organics into your pool from trees and yards. Combine that with your previously sky high CYA and the likely nascent algae in the water and you have a perfect opportunity for an algae bloom! Congratulations for getting the jump on it before it could take over the pool!
 

chessie6

LifeTime Supporter
May 21, 2010
187
East Hartford, Connecticut
All of your hard work is going to be soooooooo worth it. We had to scrub everything after having a pink algae breakout, then drain half the water to lower the CYA. There's a big difference in the water now, and the swimming is wonderful . . very soon your frazzled nerves will be no more and enjoying it all!
 

chem geek

TFP Expert
LifeTime Supporter
Mar 28, 2007
12,082
San Rafael, CA USA
If one is going to shock at high levels using a hypochlorite source of chlorine (bleach, chlorinating liquid, Cal-Hypo, lithium hypochlorite), then one should lower the pH first before doing so. Adding chlorine raises the pH. Though it will come back down when the FC level drops, you don't want the pH to get too high because it can precipitate metals that can cause staining, can cause cloudiness from over-saturation of calcium carbonate, and at much higher pH the active chlorine level goes down significantly.

The following assumes a TA of 80 and CYA of 80 and adding the amount of chlorine indicated at different starting pH. I indicate in red the starting pH that would be reasonable to keep the pH reasonably low.

10 ppm FC: 7.5 to 8.00 (active chlorine cut by 13%); 7.3 to 7.60; 7.2 to 7.43; 7.1 to 7.27; 7.0 to 7.13
15 ppm FC: 7.5 to 8.37 (active chlorine cut by 19%); 7.3 to 7.86; 7.2 to 7.61; 7.1 to 7.40; 7.0 to 7.22
20 ppm FC: 7.5 to 8.63 (active chlorine cut by 25%); 7.3 to 8.21; 7.2 to 7.88; 7.1 to 7.58; 7.0 to 7.34
25 ppm FC; 7.5 to 8.80 (active chlorine cut by 32%); 7.3 to 8.50; 7.2 to 8.23; 7.1 to 7.85; 7.0 to 7.51
30 ppm FC; 7.5 to 8.91 (active chlorine cut by 38%); 7.3 to 8.68; 7.2 to 8.49; 7.1 to 8.18; 7.0 to 7.75
35 ppm FC; 7.5 to 9.00 (active chlorine cut by 45%); 7.3 to 8.81; 7.2 to 8.66; 7.1 to 8.44; 7.0 to 8.06; 6.9 to 7.59

If you have 50 ppm Borates in the water, then you don't have to lower the initial pH by as much:

10 ppm FC: 7.5 to 7.71 (active chlorine cut by 7%); 7.3 to 7.49; 7.2 to 7.37; 7.1 to 7.25; 7.0 to 7.12
15 ppm FC: 7.5 to 7.81 (active chlorine cut by 9%); 7.3 to 7.60; 7.2 to 7.47; 7.1 to 7.34; 7.0 to 7.20
20 ppm FC: 7.5 to 7.91 (active chlorine cut by 11%); 7.3 to 7.71; 7.2 to 7.58; 7.1 to 7.44; 7.0 to 7.28
25 ppm FC; 7.5 to 7.99 (active chlorine cut by 12%); 7.3 to 7.81; 7.2 to 7.69; 7.1 to 7.55; 7.0 to 7.38
30 ppm FC; 7.5 to 8.06 (active chlorine cut by 13%); 7.3 to 7.91; 7.2 to 7.80; 7.1 to 7.66; 7.0 to 7.50
35 ppm FC; 7.5 to 8.13 (active chlorine cut by 15%); 7.3 to 7.99; 7.2 to 7.89; 7.1 to 7.77; 7.0 to 7.61; 6.9 to 7.42

The bottom line is that when shocking by adding more than 10 ppm FC, one should lower the pH to at least 7.2 first. If shocking by adding more than 20 ppm FC, lower the pH to 7.0 first. You need to lower the pH before you add the chlorine so that you will be able to measure the pH accurately since the pH test will not be reliable when the FC is much above 10 ppm.
 

Beez

LifeTime Supporter
May 19, 2009
785
Dallas, TX
chem geek said:
If one is going to shock at high levels using a hypochlorite source of chlorine (bleach, chlorinating liquid, Cal-Hypo, lithium hypochlorite), then one should lower the pH first before doing so. Adding chlorine raises the pH. Though it will come back down when the FC level drops, you don't want the pH to get too high because it can precipitate metals that can cause staining and at much higher pH the active chlorine level goes down.
:
:
:
The bottom line is that when shocking by adding more than 10 ppm FC, one should lower the pH to at least 7.2 first. If shocking by adding more than 20 ppm FC, lower the pH to 7.0 first. You need to lower the pH before you add the chlorine so that you will be able to measure the pH accurately since the pH test will not be reliable when the FC is much above 10 ppm.
This seems like information that should be in Pool School.
 

4JawChuck

Well-known member
Jun 13, 2010
223
Winnipeg, Manitoba, Canada
I agree, those corrections should be included in pool school...thanks for those numbers Chem.

The algae bloom is completely under control and gone, I managed to get an early start today and took another 12" of water out of the pool while I kept the FC high and in shock.

Check out these numbers! :)

FC-30
TC-30
CC-0
PH-7.1
CH-100 (should be around 170-200 tomorrow since I added 7KG of calcium this evening, I need another tub to get it in line)
TA-80

and the piece de resistance...

CYA-55!

I nearly did a little dance in the sunroom and I believe there was whoop and holler bellowed when I did the testing! :whoot: :party:

Needless to say I am elated with the results, I figure I dumped nearly 79000 litres of water getting it there (9000 of that was fill water) but it was worth it. The water is crystal clear and except for the shock level it should be ready for bathers tomorrow afternoon once the sun burns off the extra FC. I still need to get more calcium to bring that spec inline but I didn't want to change the PH until that is done in case I mess something up doing more than one thing at a time. I imagine once the FC burns off I will have to raise the PH into acceptable range but I am not sure what will happen once the shock level chlorine is gone, still learning how all these chemicals affect one another...steep learning curve!

I will say keeping the pool in shock while I drained water made it less stressful although at the CYA levels I started at it would have required a truck full of bleach to get it there. I am lucky I had time to do this while I was on holidays to be there to react to the bloom, it could have been much much worse. All that shock level backflushing must make my sand the cleanest in the city. :lol:

Learned another little tidbit of information that might help someone else faced with this situation, when filling with cold fresh tap water block off the deep end drain and place the fill hose at the bottom of the deep end and use the skimmer drain to backflush, the segregation of cold and warm water helps reduce the amount of fresh water sent out to the street if you draw from the warm top of the water column in the shallow end...its a small amount but significant when its your money going down the drain. Another trick I figured out is use the water slide hose feed line to drain water while you fill, it slows down the speed at which the water level goes up and if your dumping water from the backflush hose onto the street it annoys the neighbors less since I could run a hose from the slide directly to the street drain, just a little less unsightly for sensitive neighbors who see huge amounts of water getting dumped for days at a time that wets the street.

One week of holidays left, and I have you folks to thank for making all this possible. I can't imagine what it would have cost had I called a pool company to resolve the issue. I figure I have about $125 in chemicals invested and another $100 in water in the pool (thank god water is cheap here) and about 4 days time monitoring and doing other things around the house at the same time. I budgeted $1000 to resolve this as a worst case scenario and I came way under that estimate just by reading pool school and the posts on the forum.

Now I can get down to a daily regimen and figure out how much I need to add daily to maintain the FC so when I am away from home with work next month I can give the wife a schedule to work so things don't get out of control. She and the kids have been saints while I got the pool "fixed" and I have been teaching all of them all about how the pool mechanicals function and what the testing says etc...the pool calculator is an invaluable resource for teaching and reference.

Hope you don't mind if I hang around and ask dumb questions, still lots to learn...but I think I need a drink first. :cheers:
 

Isaac-1

TFP Expert
LifeTime Supporter
May 10, 2010
6,711
SW Louisiana
A lot of people will tell you that there is no reason for CH in a vinyl lined pool, I like to keep it in mine to protect the concrete decking, and grout around the pool area from splash out. I have very soft water, and bringing up the CH seems like it is cheap insurance.

Ike
 

PaulR

LifeTime Supporter
Jan 11, 2009
1,966
Cupertino, CA
4JawChuck said:
the segregation of cold and warm water helps reduce the amount of fresh water sent out to the street if you draw from the warm top of the water column in the shallow end
The simultaneous fill/drain technique is a good trick to know. I've seen a few reports now; once you balance the fill and drain rates you can go quite a while with it. And of course you get the biggest bang for the buck by draining as much as possible in one round.

What caught my eye, though, was "out to the street..." Many areas in the US require draining to the sewer, not the street. You might check with your local water department.
--paulr
 
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