Cyanuric Acid Gone Wild

[jetdoc]

Howdy All,

I'd like to get the lowdown on Cyanuric Acid. Just had it tested @ my local Leslie Pool Supply and told my CYA was 300ppm. Told to immediately drain off 2/3 and refill. So after draining down my crystal clear water, I'm filling up and will retest in the morning. My stats prior to draining were:

FAC .5

TAC .5

pH 7.5

TA 130

Calcium Hardness 350

CYA 300

This is my second swim season as a pool owner, so I was wondering, is it normal to need to drain down a pool every couple of years due to using stabilized tabs and powerpowderpro for shocking? What else can cause cyanuric acid to accumulate in a pool? Here in central TX, we've had tons of rainfall the last few months. Can this be a factor?

Looking at a Water Analysis Form from last season, I noticed a CYA reading of 100, but it wasn't mentioned to be a concern. This time though,(same place, different kid) was told that if my CYA hits 100, that's the time to start draining and refilling.

Wouldn't it be better to use non-stabilized chlorine powder when it hits the 100 mark instead of selling me more CYA stabilized products?

Also noticed recently, that even the next day after shocking the FAC & TAC are still in the low ranges. Where is my chlorine going? Is it still in the pool, being shut out by the cyanuric acid. I've noticed the yellow algae seems to appear quickly and consistantly, requiring more frequent brushing and vacuuming.

Any help in understanding cyanuric acid levels would be greatly appreciated!!!

LD

[chem geek]

My responses to your questions are in bold.

Howdy All,

I'd like to get the lowdown on Cyanuric Acid. Just had it tested @ my local Leslie Pool Supply and told my CYA was 300ppm. Told to immediately drain off 2/3 and refill. So after draining down my crystal clear water, I'm filling up and will retest in the morning. My stats prior to draining were:

FAC .5

TAC .5

pH 7.5

TA 130

Calcium Hardness 350

CYA 300

You are very fortunate that you did not get algae with the high CYA and low FC level. Either you had some sort of algaecide (PolyQuat or Copper) or had a shortage of nutrients in your pool (e.g. phosphates).

This is my second swim season as a pool owner, so I was wondering, is it normal to need to drain down a pool every couple of years due to using stabilized tabs and powerpowderpro for shocking? What else can cause cyanuric acid to accumulate in a pool? Here in central TX, we've had tons of rainfall the last few months. Can this be a factor?

If the rainfall caused overflow of the water from the pool, then that would dilute the CYA reducing it. If it just raised the pool level while the sun with evaporation brought it back down, then the water chemistry would not change except to increase items that come in with new fill water if evaporation continued that far.

I also suspect that you may have a cartridge filter since a sand filter that gets backwashed weekly would tend to dilute the pool water more rapidly so that the CYA wouldn't build up so quickly.

Looking at a Water Analysis Form from last season, I noticed a CYA reading of 100, but it wasn't mentioned to be a concern. This time though,(same place, different kid) was told that if my CYA hits 100, that's the time to start draining and refilling.

Wouldn't it be better to use non-stabilized chlorine powder when it hits the 100 mark instead of selling me more CYA stabilized products?

Generally yes. I wouldn't even wait until the CYA gets that high unless you maintain a minimum FC level of 7.5% of the CYA level to prevent green algae. Usually 30-50 ppm CYA is sufficient. If you need to shock the pool to get rid of algae, it takes a LOT more chlorine at the higher CYA levels since shocking to quickly remove algae takes an FC of around 40% of the CYA level (20% works, but much more slowly). The other alternative is to use a weekly PolyQuat 60 algaecide to keep away algae (or an expensive phosphate remover or a copper algaecide or copper ionization, but that has side effects if the pH goes up).

Unfortunately, there are not great options for unstabilized chlorine in terms of automatic dosing in floating or in-line feeders. Stabilized chlorine such as Trichlor, as you know, dissolves slowly, but for every 1 ppm FC added by Trichlor, it also adds 0.6 ppm to CYA. Dichlor, which dissolves quickly, is even worse where for every 1 ppm FC it also adds 0.9 ppm to CYA. Cal-Hypo is usually granular, but must be pre-dissolved in a bucket of water though there are HTH Duration Tabs you can get that dissolve slowly BUT tend to fall apart near the end and leave a residue. Also, Cal-Hypo increases Calcium Hardness (CH) though it does not increase CYA. For every 1 ppm FC added by Cal-Hypo, it increases CH by 0.7 ppm. In percentage terms, this is better than the increase in CYA with Trichlor/Dichlor since CH is usually higher and not as much of a problem.

The only non-liquid that does not add to CYA nor to CH is Lithium Hypochlorite, which is a fast-dissolving powder, but this is VERY expensive -- about 5 times the price of the equivalent amount of Trichlor (in terms of FC). That leaves unscented bleach or chlorinating liquid which are identical except for concentration (strength). These do not add to CYA or CH. The only side effect is that all three (lithium hypochlorite, bleach, chlorinating liquid) do add extra salt. All sources of chlorine add salt since the chlorine itself gets converted to salt where 1 ppm FC gets converted to 0.8 ppm salt (as chloride) when the chlorine gets used up. But these three hypochlorite sources of chlorine add an additional 0.8 ppm of salt to the pool. This is not a problem as it just very slowly increases Total Dissolved Solids (TDS). Remember that salt pools with a saltwater chlorine generator (SWG) have around 3000 ppm salt.

Without slow dissolving forms of chlorine you may need to add chlorine to the pool nearly every day or two. If you have a pool cover that shields the water from the UV rays of the sun, then you may only need to add chlorine every 3-4 days. For automation of adding chlorine, you can consider using The Liquidator.

Also noticed recently, that even the next day after shocking the FAC & TAC are still in the low ranges. Where is my chlorine going? Is it still in the pool, being shut out by the cyanuric acid. I've noticed the yellow algae seems to appear quickly and consistantly, requiring more frequent brushing and vacuuming.

Well, there's the answer to the question of why I wondered why you weren't seeing algae -- you actually are. In fact, you are on the edge of an algae bloom and your chlorine is getting consumed fighting the algae. Again, you are lucky that it didn't take off more quickly. If you truly have yellow/mustard algae instead of green algae (yellow/mustard algae is more like a powder that usually starts growing on the shady side of the pool while green algae is usually free-floating), then that takes even more chlorine to keep away -- an FC level of 15% of the CYA level -- and it takes more chlorine to shock to get rid of -- an FC level of 60% of the CYA level -- so it's really something to deal with only after you've gotten your CYA level way down. There are algaecides to deal with it, but copper is best for it yet has the side effect or precipitating at higher pH as green water and stains and can make blond hair have a green tint -- bromine algaecide also works for it while the quats are less effective, though still work better than nothing.

Any help in understanding cyanuric acid levels would be greatly appreciated!!!

Cyanuric Acid protects chlorine from breaking down by sunlight in two distinct ways. First, the CYA molecule itself actually absorbs UV rays so that it shields chlorine at lower depths of the pool. This effect seems to start to dominate when the CYA level gets up to the 40-70 ppm range. Second, the CYA molecule combines with chlorine (hypochlorous acid) to form new compounds called chlorinated isocyanurates. These new compounds are not effective sanitizers, oxidizers, but do breakdown from sunlight much more slowly. The vast majority of chlorine is bound to the CYA. Fortunately, it takes a very low level (concentration) of hypochlorous acid to kill bacteria. It takes more to kill or prevent algae. When the CYA level (in ppm) is at least 5 times higher than the FC level, then the ratio of FC to CYA determines the amount of disinfecting chlorine that is available compared to no CYA being present. So with 50 ppm CYA, one has 1/50th the amount of disinfecting chlorine in the pool compared to the same FC level with no CYA. This rule works near a pH of 7.5.

If you are interested in technical detail about all of this, you can take a look at the posts I've made in this thread.

LD

Hope that helps.

Richard

[Rhumbline]

I don't have much more to add here since the previous post really gave you the answers that you need. However, I bought a house (also in TX) last year and I am in the same position as you with CYA just not quite as high. It seems like the pool stores like to sell us overprices stabilized chlorine with no other option. Then they tell us to refill 1/2 the pool every time the CYA gets too high.

Our solution was to change our pool over to salt water at the begining of the summer. With the Salt Water system non-stabilized chlorine is generated, so you manage the CYA level yourself and don't have to worry about it getting too high. The added bonus is that the salt water system has saved us a TON of money and it looks like it will pay for itself quickly. Since going to salt water the only things we have needed were salt (cheap), Muriatic Acid (we use a $5 gallon weekly) and Bleach to shock one a month. Previously we were a member of the $150 a month club at the local pool store.

The bottom line is that you can save money on chemicals using alternate products mentioned on posts on this board. However, if you can afford a salt system it will save you money, pay for itself pretty quickly and it makes water chemistry much simpler.

Just my $0.02 after having the same problems in the same area. Send me a message if you have any questions about our experiences.