Mysteries of Cyanuric acid, free chlorine and algae

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Chas

Chas

0
In The Industry
Jun 8, 2015
31
Juneau Wisconsin
Well, this forum added an element of fun and challenge to getting my horrible pool water cleared up during the fresh fill after I replaced my liner. It took 9 days, 144 oz. of iron sequestering chemical, 2 quarts of algaecide, 6 lbs. of shock at three different times, 2 gal. (and counting) acid, 12 filter cartridge cleanings and plenty of vacuuming and brushing to get the water sparkling clear and the iron from staining. I found this forum while looking for an answer re; iron sequestering chemicals. Started filling through my iron filter – 600 gal. at a time between regenerations – on Memorial Day 5/25/15, added sequestrant and algaecide as it filled, no chlorine. First shock went in to brown water 6/7/15, went to normal operation with clear water 6/16/15.
So, here are some observations I made during the trial and tribulation of filling from my iron laden well and subsequently testing and treating the water. The topic of cyanuric acid ie; “conditioner” or stabilizer” is forefront in my mind.

  1. I bought a TF-100 test kit, got it Sat. 6/20/15 and tried all of the tests. Nice kit!
  2. I have not added any CYA until last night.
  3. I have been running the pool with Tri-Chlor tabs in my erosion feeder since 6/16/15.
  4. Fresh fill TA was 410ppm 6/8/15, now at 350ppm
  5. FC has been 4-6ppm, I took the pucks out and let it drop to this morning’s reading of 2.0
  6. pH has been as high as 7.8, this morning 6/25/15 is 7.5.
  7. No algaecide has been added since 6/15/15. No algae (or boatmen) present.
After reading here about the relationship of CYA to FC, I’m really curious about CYA. I tested for CYA with my new TF-100 last night running Tri-Chlor since 6/16/15 and find none present. The pool is using very little chlorine, I filled the feeder only halfway and have the valve turned off yet the FC has been running higher than I’d like it. The feeder is new this season.
My seat-of-the-pants observations compared with my recent few years in the 25 years of my running this pool:

  1. It’s using less CL for this time of the year than it did the last few seasons.
  2. No algae or boatmen are showing up. By this time the past few seasons I would have used at least another couple of quarts of algaecide.
  3. Thanks to this forum, I have a renewed faith in FC to keep algae out.
My question is:
Why add any CYA at all if there’s already CYA in the Tri-Chlor I’m using? I have no desire to hand feed liquid chlorine and will continue to use the feeder with Tri-Chlor. I added enough CYA last night, 6/25, to get the level to a roughly calculated 10ppm, we’ll see what it actually is when I test for it with my new test kit in a few days. I’m reluctant to get the CYA up to 30 or so if it will continue to build with time. I’m convinced that what I’ve read on this forum about the relationship of CYA and FC and algae is absolutely true and that explains what I’ve observed these past few years. I don’t want to drain 25% of my water every year or two to get the CYA back down due to my poor quality makeup water and am willing to maybe go through a little more Tri-Chlor due to too low of CYA for the first few years.


I tried to post a before and after .jpg pic but it's "Not a valid image file". Tried a couple different sizes and formats, got the same results. Maybe the server isn't fully up yet?
 
Well Chas, in regards to your concern about CYA, I supposed the TFP veterans or Chem Geek may chime in later. I've seen all sorts of posts about the chlorine/CYA ratio added to a pool each week/month by using tablets. In essence though, as basic as I relate to this subject, a pool's demands of FC each and every day is directly related to the CYA protecting it. Yes, tablets can be used to increase CYA, but they are slower than adding directly (via sock method), and you run the risk not only of going through a lot more chlorine until the CYA is at the proper level, but leave the water unprotected from organics/algae. As you have stated, the TFPC methods do indeed work, and work well without algaecides or other pool store products "if" the proper FC/CYA ratio is maintained. Some pool owners simply chose to follow a different method, and to that end we wish them success and an enjoyable season. All we can do is speak for TFPC methods and their proven years of success.

As for posting pictures, have you tried linking your photos from Photobucket? That's what many of us do here on TFP. Upload your pics to Photobucket (free), then copy & paste the IMG code for that pic from Photobucket to your TFP post. Works great.
 
For every 10 ppm Free Chlorine (FC) added by Trichlor, it also increases Cyanuric Acid (CYA) by 6 ppm. That's a chemical fact independent of concentration of product or of pool size. If you were to have a daily chlorine demand of 2 ppm FC per day with Trichlor as your only source of chlorine, then this is an increase of 36 ppm per month. So without water dilution, it doesn't take long to get the CYA too high. In my own new pool 12 years ago using Trichlor for chlorine, my CYA rose from 30 ppm to 150 ppm in one and a half seasons and that was with a rather low 0.7 ppm FC per day usage due to a mostly opaque pool cover.

You can certainly use Trichlor to build up the CYA. In the early stages with low CYA, you will lose a lot of chlorine to sunlight (if your pool is fully exposed) so you just need to be aware of that. Once the CYA builds up more, then you will be fine for a while but as the CYA climbs you'll need a higher FC level to prevent algae growth (unless you use supplemental methods at extra cost). You will still be OK, but if things go south for whatever reason and you have a high CYA level, then fixing the problem is harder due to the higher FC levels that are then required to SLAM.

If you want to get "a few years" with your strategy, you'd need to use a mostly opaque pool cover to significantly cut down chlorine loss from sunlight. Otherwise, the CYA level will climb pretty quickly. You might get lucky and lose CYA over the winter if you let the pool go with bacteria converting it hopefully to nitrogen gas but they could also convert it to ammonia in which case you'll have a HUGE chlorine demand upon opening. If you close your pool in a way to avoid this (say with elevated chlorine followed by Polyquat 60 and closing and opening when the water is cold < 50ºF) then your CYA will mostly only drop some from water dilution over the winter.
 
We've talked about using polyfill or batting material to filter out oxidized iron. Note that the video is starting out with solid iron oxides. If you have a skimmer, you don't need to make a bucket filter but can use polyfill or batting in your skimmer. Alternatively, if you have a decent filter you can filter out the iron into it instead though using the polyfill or batting is easier since you don't need to clean/backwash your main filter.
 
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