Questions/comments newbie, Phosphates/CYA/Flocs/Clorine

[Mikel]

I have some questions after reading several postings on here.

First, I have 14K gallon plaster pool with DE filter about 4 years old.

My CYA has always been pretty high, 80+, last year early, over 100, this year can't measure, but probably at least 150+. I know this is too high, and I just drained over half my water. I'll measure after refill.

However, I've never had an algae problem and I usually maintain 2-3PPM using tri-clor tabs. According to this site, with my high CYA, I should have a green pool? 2 of the years, I started the season with a Nature-2 system, but those don't last all summer, so I don't know how much that helped.

Also, last year, for the first time, I measured Phosphates, just because I read about it on the web.. wasn't having any problems. Used Phosfree to get the level down from 3000+ to 200. However, couple weeks later it was up to 1000 again. No leaves, minimum grass blow from mowing, etc. I think its impossible or very expensive to keep this level down. It also clogs up the filter immediately.. I think I'm going to forget about phosphates.

For floc treatment, this site says, let it settle for 24-48 hours, and carefully vacuum it up. Why not let it get caught in the filter while running, then just backwash it out?

I'm thinking of switching to the BBB system and/or a SWG. The CYA is impossible to control using traditional methods.

Question, (I live near Dallas). If I go the BBB route, how much bleach am I going to have to buy/store to keep the FC up? Will I really need 10-15ppm to keep algae out? Normally, for me, this is shock levels.
If I go with a SWG, I'll only need to BB method right? since I'll have the chlorine method handled.
I have a heater/spa attached. Right now the in-line chlorinator after the valve when in spa/heat mode.. this keeps from burning up the tabs when heating. Can the SWG in-line piece handle the hot water? I don't have the plumbing room to put it after that valve. Does anybody know if the electrical is easy for the hookup, i.e. DIY?

Sorry for so many questions, I didn't want to track multiple threads.

Thanks! Mike

[chem geek]

Algae growth is not guaranteed just because the CYA level gets high. There can be other factors limiting algae growth including nutrients such as phosphates and nitrates as well as sunlight and the presence of algaecides. Last, but not least, is that there is no such thing as spontaneous generation so algae won't grow unless it gets introduced into your pool in the first place.

Nature2 contains copper metal ions (plus silver or zinc) and the copper is a strong algaecide. The downside is that copper can stain plaster surfaces and make blond hair have a yellow-green tint. These problems are more likely to occur if the pH goes up.

Chlorine alone can keep algae from growing and the general rule of having a minimum Free Chlorine (FC) level that is at least 7.5% of the Cyanuric Acid (CYA) level seems to work up to a phosphate level or around 3000-4000 ppb. Since in your case you measured such high phosphate levels and didn't have algae growth even though your FC was from 1.5-3% of the CYA level, then the other factors helped (Nature2, possibly low nitrates, no initial algae, etc.). The copper from the Nature2 won't go away quickly so could have lasted longer than you expected -- it depends on the rate of dilution of water in your pool. I suspect that's the main thing that's been helping you out preventing algae.

As for floc, it consolidates particles strongly so they tend to settle at the bottom of the pool even if you had circulation running. If you use a clarifier instead, then this is less powerful at clumping so the consolidated particles tend to get caught in the filter and you can backwash as you described. Generally, for mild cloudiness, a clarifier will work, but for heavier problems, a floc is more effective. However, neither one is needed if you have patience and use shock-levels of chlorine as chlorine will generally break down (oxidize) algae that is the primary source of cloudiness (assuming the cloudiness isn't over-saturation of calcium carbonate).

Yes, with an SWG, that takes care of one of the "B's" -- you won't need bleach (or chlorinating liquid). The SWG is usually placed as the last item in your system so that there is nothing downstream that will be exposed to higher chlorine levels. The SWG can handle hotter water, but there is a greater risk of scaling with hotter water so if you can have the SWG off during high heating that would be better. Otherwise, you can run your saturation index slightly more corrosive to prevent scaling -- if your pool is vinyl, then this is not an issue as you can just have a much lower Calcium Hardness (CH) level. Others can answer your installation questions as I don't have an SWG myself.

Richard

[Guest]

I had read that Nature 2 only puts like .2 ppm copper in the water so it shouldn't cause staining and such. However, my plaster did start to turn bluish/aqua last summer and I tried to use Jacks #2. Seemed to clear it up, but this spring it was worse, and the water actually started to look dark blue. 1st, Leslies shouldn't have told me to use #2 since I have a heat exchanger. I think my heat exchanger is now worse. I've installed bypass on the heater so when I'm not using it, I'll keep the copper out. This may also have helped my algae from forming. I'm using metal-out now to try to remove some of th e staining, so I can't use nature-2 until that process is done.

I'm surprised that more people don't have algae problems with the normal 60-80ppm CYA and 1-3ppm chlorine the stores recommend/measure.

I was more worried that when heating the spa 120+ degree water would be bad for the SWG, I wonder if it turns itself off over 104. Just read the AutoPilot works up to 104... didn't say what happens if you go over.

Sometimes, when I leave debris in the sweeper, he will get a little algae on the netting, so I know there is a little bit in there..

Thanks for the info, Mike

[chem geek]

I'm surprised that more people don't have algae problems with the normal 60-80ppm CYA and 1-3ppm chlorine the stores recommend/measure.

I was more worried that when heating the spa 120+ degree water would be bad for the SWG, I wonder if it turns itself off over 104. Just read the AutoPilot works up to 104... didn't say what happens if you go over.

Sometimes, when I leave debris in the sweeper, he will get a little algae on the netting, so I know there is a little bit in there..

Mike,

If you look at the algae section in The Pool Forum and poolcenter.com and Trouble Free Pool and this forum, you'll see plenty of examples of pools with high CYA levels getting algae. Also, spend some time at your local pool store and see how many people come in reporting algae and are sold algaecides and other treatments. Again, it's a probability thing with multiple factors. If one is at the higher end of the 1-3 ppm FC range and is below 80 ppm CYA, then only those pools with higher nutrient levels (phosphates and nitrates) and proper amounts of sunlight will get visible algae. So many pools won't until the chlorine gets closer to 1 ppm FC or >100 ppm CYA at which point most pools have enough nutrients to have algae growth be faster than chlorine kill rates of algae. Of course, if one is using an algaecide such as PolyQuat 60, phosphate remover, copper, then that lowers the algae growth rate such that lower chlorine levels are able to kill algae faster than it can grow.

By the way, the normal recommendation for CYA is not 60-80, but 30-50 ppm (with a max of 100 ppm) and the later NSPI standard range was 2-4 ppm FC as shown here. The 60-80 is for SWG pools and that's a different situation. In such pools, there is superchlorination of a portion of the water passing through the SWG cell and that kills a lot of free-floating algae so in such pools the minimum FC level is around 4.5% of the CYA level instead of 7.5% for manually dosed pools. The more consistent dosing plus the superchlorination of part of the water allows for a lower FC/CYA ratio to accomplish the same algae killing rate. There are also reasons for having the higher CYA to slow chlorine breakdown from sunlight in SWG pools as that lets one lower SWG output which lowers aeration from the hydrogen gas bubbles produced in the SWG cell and the rate of pH rise in such pools since that is due to the outgassing of carbon dioxide from the pool (pools are intentionally over-carbonated).

The chlorine kill rate of algae is a function of the hypochlorous acid concentration in the pool. This is known science since at least 1974 and the disinfection and oxidation capabilities of chlorine have been confirmed in numerous scientific studies to be proportional to the hypochlorous acid concentration and not to the Free Chlorine (FC) level. It is the ratio of FC to CYA that roughly determines the hypochlorous acid concentration and therefore determines the likelihood of algae growth, all else equal. It also determines the disinfection rate, but most bacteria and viruses are incredibly easy to kill so require very little chlorine -- it's algae that usually requires more chlorine to keep from growing. Protozoan cysts (Giardia and especially Cryptosporidium) require a lot of chlorine to inactivate, but have to be introduced into water from an infected person (via fecal matter).

If you are interested in the technical aspects of the chlorine/CYA relationship, you can learn more about that here.

OK, now I understand your concern regarding the heater -- I was thinking pool temps, not spa temps. You are right that you should check with the SWG manufacturer to see what should be done in that situation. I don't know if they automatically shut off or not, but you could hook something up to turn off the SWG when heating the spa, if that's easy to do.

That's interesting about getting algae in the debris in the netting since I would expect that to be exposed to chlorine as well, but perhaps the circulation is poor "inside" the pile of debris so the chlorine gets depleted locally. It does sound like your pool has nascent algae, but is being kept in check by the chlorine and small amount of copper. In fact, long before algae is visible, algae growth can be seen as an unusually higher amount of chlorine demand, even if the water appears clear. Algae is only visible when there is enough of it to diffract light at which point the water starts to look dull, then cloudy, and eventually light green and then dark green when enough algae is clumped together in thickness to make the chlorophyll in their cells visible.

Richard