Algae and CYA

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R

radaklj

0
May 26, 2016
8
Anaheim, CA
Hello,
I am new to this forum, however I have been a pool owner for 43 years and have owned my current pool for 39 years. I have maintained my pools—pool chemistry, cleaning, etc. myself during that time. I live in Southern Calif. (Orange County).

During the past two or three summers, I have experienced an algae problem that I never experienced before. Green/yellow algae on the walls (plaster pool), need for constant brushing, filter plugging and backwashing, sanitizer usage, etc.

After a lot of reading and research, I came to the conclusion that my problem was high CYA levels combined with too low levels of FC (2-3 ppm). I was carrying CYA levels of 80-100 ppm, (recommendation of pool store) or more, and using tri-chloro tabs for chlorine stabilization, not realizing that was also increasing my CYA (the past year, I have stopped using the tabs and now use liquid sodium hypochlorite). According to the info on this website, and others, the higher the CYA levels, the need for higher FC to afford good protection.

In the last two or three months, I have strived to get my pool in proper balance (pH, TA, FC, CYA, CH). I drained nearly 1/2 of my pool (and this is a problem since I am in a drought zone and constrained on my water usage). Here are my current pool metrics:
pH 7.6
TA 90
FC 2-3
CYA 60 - 70
CH 800 (I realize high but again constrained by drought situation)

As I write this my pool looks great. But with summer approaching, I am dreading the return of my algae problem. According to the info on this website, with a CYA of 60, I need to maintain a FC of 5ppm. With this background info, I have a few questions of which the first is the most important.

  1. Assuming my hypothesis is correct about the relationship between CYA/FC/Algae, do I need to bite the bullet and maintain a 5ppm FC this summer to avoid an algae problem? It will require a lot of liquid chlorine (and acid since I believe that sodium hypochlorite raises pH and low pH enhances chlorine’s effectiveness). I am willing to do this unless there is an alternative I am not aware of. Is a FC of 5 safe for swimmers?
  2. During the last few months in which I mentioned earlier that I was trying to achieve proper pool chemistry balance, I have added a lot of acid. Originally my pH was 7.8+ and the TA was 100 or higher. Every other day I check pH, FC, TA and acid demand. I am adding on average 3 pints of acid every other day (38,000 gallon pool) with no change in pH or TA. (As mentioned earlier my current pH is 7.6 and TA is 90 but seems to be stuck there). The only reason I am adding acid is because the acid demand test indicates a need for it. Am I on the verge of a huge breakthrough in either pH or TA or is something else going on?
  3. I do not understand why I have not experienced this algae problem in all the years I have maintained my pool(s) except for the last three or four. Any insights on this?


  1. Does the high CH have any bearing on any of this?


  1. Is it necessary to shock a pool on a routine basis? I was using a shock product (di-chloro) on a minimal basis the past few summers, more as a clarifier and floculator rather than a chlorine agent. Should I shock even if I do not have a visible algae problem (keeping in mind that de-chloro, I believe, increases CYA).

I realize this may be a lot to digest, but I felt compelled to provide as much background info in order to reduce the amount of guessing on my situation.
 
Hello and welcome to TFP! :wave: Let me get right to your questions:
1. The higher FC is fine. When FC matches its current CYA counterpart, the CYA serves to protect the swimmers and pool equipment. In fact, if you ever have algae at that CYA, you'll see the approved FC SLAM level is much higher and still safe for the pool. I maintain a CYA of 60-70 and my FC is always in the 6-8 range.
2. I suspect your acid demand may be because of the TA. We have found that by lowering TA even further, sometimes from 70 down to 50, it stabilizes pH much better and reduces the amount of rise.
3. Hard to tell. Luck? Weather, products added, chemical levels at that time? But eventually the higher CYA catches-up to everyone. That's a big reason they end-up here at TFP
4. No. CH will have a bearing on your calcium saturation index (CSI) and potential for scale (high CH) or potential for damaged plaster (low CH), but not algae.
5. No. Because TFP pools are maintinaed at the proper FC/CYA ration 365 days per year, there is no algae, no excessive combined chlorines or organics that require such treatment. In the event something happens to a pool and it does get algae, we perform a "SLAM" (link below in my sig).

Hope that helps, great to have you with us.
 
Your hypothesis is correct. Maintain adequate FC for the CYA and algae won't grow. I'm not all that far from you and I typically lose about 2 FC per day. You have a gigantic pool, so it's going to take a good bit of bleach. See if there's a HASA dealer near you. The stuff is 12.5% and always fresh and the jugs are returnable so your trash can won't be choked with empty bleach jugs.

Your acid use sounds about right. The problem is aggravated by high TA in the refill water. Over time, I've learned how much acid to add for each inch of water I add, and I pour it into the hose stream when I fill. If you plug all your numbers into poolmath and then scroll down to Effects of Adding Chemicals, you can see what effect the acid will have on the TA when you reduce pH. The pH calculation down there isn't as good as the one above. Ignore it. The TA calculation has always been right on the money for me. You'll see how small an effect it has on the TA and why the reduction doesn't always register on the test.

The algae, maybe just good luck? Maybe someone carried some spores from a lake or someone else's pool in on their swimsuit?

High CH only affects the risk of developing Calcium Scale. It doesn't impact any other chemical readings. 800 is high, but manageable. Mine is higher, and I haven't replaced the water for reasons you're all too familiar with.

No, you don't need to shock on a regular basis if you maintain adequate FC. The only time I boost the FC is before a big party, before I leave town for more than a couple days, or after a big windstorm when lots of stuff gets blown in the pool. The only algae I've ever had in five years was a small amount right in the grout at the water line inside the skimmer throat. I just scrubbed it off. I don't think I've ever been at shock level in all that time.
 
Welcome to TFP :) great job on what you have already seen and figured out :)

CYA, keep your FC at target of 8 never let it get below 5 Pool School - Chlorine / CYA Chart

Poolmath is now your friend :) it will tell you exactly what you need, put your numbers in the now column and put your target numbers in, use TFP, bleach, and plaster in the bottom

try to keep your CSI in the -0.3 to 0.0 range and your CH should not be a problem

You can swim up to SLAM level with no issues, so for your CYA level 28 fc

try taking your TA down to 80 and see if your ph stays steady if it is still raising try 70.. this will keep your acid addition to a minimum... Pool School - Lower Total Alkalinity

keeping FC at 8 will take a lot of chlorine/bleach, 12.5% will make it less to add but still a lot.. you can do 2 things that will make it easier

1. I know this is almost impossible: drain 30% of your pool, this will drop your CYA to about 30 and also drop your CH ( unless you have high CH fill water) CYA of 30 your FC would be 4 and stay above 2 at all times.. you can also do this by backwashing a little longer every time, it may take this summer but it would lower your CYA..

2. a salt water generator: your CYA is almost perfect for a SWG and it will add chlorine by itself, no hauling gallons of liquid chlorine.. they now have SWG that can create 3 pounds of chlorine a day.. the new RJ 60 plus also has a 15000 hour cell..
CircuPool® RJ-60 Salt Pool System

if you decide to go this route by the RJ 45 plus and add the 1 dollar upgrade to the 60
CircuPool® RJ-45 Salt Pool System

I hope this helps :)
 
I appreciate all the comments. Looks like I need to focus on increasing my FC and perhaps trying to get my TA down in the 60-80 range. Is adding just acid to lower TA adequate, or should I try the acid/aeration method described in TFP?
 
Acid is perfect for lowering TA, but it also lowers pH. So that's where the acid/aeration method comes into play. Lower pH to about 7.0-7.2, then see how far it lowered TA with it. Increase pH with aeration which leaves TA untouched (lower). Continue as required. :)
 
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