Hi all! I have been running my SWG for 5 years and never had to fool much with my pool chemistry at all, but the cell died this winter leaving me a huge mess to clean up in order to open the pool...Until I can re-plumb for the new SWG cell, I'm running Tri-chlor tabs with Cal-Hypo for the occasional shock/FC booster, and have had to get myself educated to a whole new sanitizing process...

Anyway, that's how I found TFP...I have really enjoyed many of the posts, as I tend to really enjoy getting a lot of nitty-gritty details. In reading posts, though, I've developed several "I now know just enough to be dangerous" questions that I can't find answers to easily:

1) Some folks seem to post that they have/maintain FC levels well above 10 between regular maintenance cycles...or at least while they're shocking algae and watching for overnight FC drops....I was of the impression (from pool store guy) that FC>10 was problematic for bathers, as it could penetrate skin at that concentration (osmosis, I guess?!?) At what point is FC level too high for bathers? Is the reason for waiting to swim after shocking due to the need for FC to drop, or just to allow shock to disperse fully, so that bathers don't encounter stratospheric FC levels, or just to avoid being in the pool during really rapid oxidation phases?

2) I use a Taylor-2005 kit...and it only measures FC up to 5...using R-0001, R-0002, and R-0003 reagents....Are those the same reagents mentioned on the site that are used to test higher FC levels, and I just don't have a good enough color comparator, or would I need diff agents to test above 5?

3) I was totally surprised to hear in some posts that CYA apparently works differently than I was led to believe for the past 5 years...If FC levels have to be higher with more CYA in order to have the same sanitizing effect, what is the real "purpose" of CYA...does it really do anything helpful (e.g., is the CL that it "Locks up" eventually "unlocked" if it's really needed for sanitizing?)? In other words, is CYA really needed at all, or does it just give pool owners a false sense of security thinking that they have some FC when they really don't?

4) Backwashing/Cleaning CYA away -- Before TFP, I'd never heard of getting rid of CYA being a problem, as I have to replace my stabilizer seemingly every year! I once heard an old-timer near me opine that CYA tends to congregate on a DE filter...and not just during its initial (long) dissolving process....and that it can be pretty easily washed away from even reasonable amounts of backwashing. Has anybody else had that experience?!? Granted, my low CYA issues on opening may be because of ammonia issues (long story, but I'm usually really lazy with maintenance during winter months, and ammonia is possible...though I've never tested for ammonia) or it may be because I lose all of my CYA when I really clean my filter grids at the start of every season...I have noticed that if I take the filter apart and really wash the grids mid-season (e.g., post a massive algae bloom that always comes when my mother-in-law has large parties while I'm on vacation!), I always lose CYA big-time...so the rumor about CYA congregation on the grids seems to hold some merit in my experience. Anybody else have similar experience?

5) My CH is really low right now (not sure why), but I think that's a good thing since I'm just starting to use Cal-Hypo as a shock/source of FC. Will Cal-Hypo have the positive side-effect of actually increasing my CH appreciably? Some folks's posts seem to suggest so...

Thanks - I'm really anxious to hear everybody's thoughts on the above!

Brian

1. FC level would depend on the CYA level. You wouldn't be swimming (I hope) when you are shocking though!

2. No, you need a FAS test kit instead of your DPD to measure high FC levels.

3. CYA buffers FC, releasing it as needed. Someone else might be able to describe this better.

4. The only time I've heard of CYA being washed out of the filter is when it's not fully dissolved. Backwashing would cause some CYA loss due to the water being removed from the pool and replaced with tap water, but it's not the same as washing it out of the filter.

5. Yes, Cal Hypo will raise CH.

Higher CYA levels reduce the total amount of chlorine you need to use. However they raise the FC level you need to maintain. I know, it is counter intuitive, higher FC level but less total chlorine used. However, when CYA levels get too high there are various problems/side effects, for example with CYA at 100+ it becomes exceedingly difficult to get rid of algae once you have it, so you don't just want the CYA level extremely high.

CYA sometimes goes away over the winter, which is why you often need to add some at the start of the season.

Welcome!!!

Many of your questions can probably be answered in Pool School (see upper left of forum page).
I am sure someone will come along with much more detailed info, but here are my quick thoughts:

1) The required FC level to maintain a sanitized pool is directly related to the CYA level. For example, with a CYA of 100 (not unheard of, but typically too high based on this forums recommendations) you need to maintain a FC of between 8 and 13 normally and a shock level of about 25. It is generally said here that you are safe to swim up to shock levels. You can see this recommended levels in Pool School and at http://www.poolcalculator.com

2) The kits recommended here use a FAS-DPD test for the FC and CC levels. That is different than what you have and can test levels up to 50ppm(?) I think. There is no color matching. You add drops until the pink turns clear and the FC level is based on number of drops.

3) I do not fully grasp the CYA either, but mainly it protects the FC from being broken down by sunlight ... thus indoor pools generally do not need it.

4) Only way to lower CYA that I am aware of is thought water changes, so a lot of splash out and frequent long backwashes could lower the level. I guess another possibility is the ammonia breaking it down or something in extreme cases.

5) What does low mean? I am sure you will be asked to provide a full set of numbers before anyone recommends a certain product or remedy. However, you are correct that if you have low CH, the cal hypo will increase CH.

I think the Taylor 2005 is pretty good but for the lack of the different chlorine test. So, you may be able to provide most of the needed chemistry levels that more experienced forum members will want to provide guidance.

ETA: Apparently my quick thoughts are still too slow

Thanks for the great input Robbie! I'm curious to see if others can fill in more details too - esp on the mechanism by which CYA releases CL if it's needed, as the various posts I've read aren't very clear on whether that happens or not!

As for the FC question you asked, no, I'm not *intentionally* swimming at high FC levels right after shocking, but my FC test only goes to 5, and I'm maxed out on the color scale currently, so all I really know is that I'm north of 5, but not by how much...In the past, with my SWG, I've always maintained FC ~2, and any time I've super-chlorinated/shocked, it was purely to burn off Chloramines that I knew were there, so I've never actually seen a FC level stay at/above 5 for any length of time. BUT I've had heavy bather load over past week, coupled with high temps and some stubborn "Die Hard" algae, so I've been shocking and brushing a LOT this week trying to get things totally "normal"...When I noticed yesterday/today that FC (finally) isn't dropping back down below 5 really quickly after shocking, it raised the (new to me) question of whether I can/should allow the kids to swim or not when all I really know is that FC is >=5 and that it could conceivably be as high as 15 (not likely, with all the sun we're getting, but a max based on the Cal-Hypo I threw in)...it's been 24 hours since last shock and FC is still somewhere north of 5 (CYA is currently somewhere between 5lbs and 9 lbs in 28000 gallons)...and so now I'm starting to wonder if the usual instruction not swim after shocking is due to the need to get FC down to "normal" levels (say around 3-5 for typical CYA concentrations), in which case the kids can't swim, or something else altogether (like avoiding high FC concentrations initially, or rapid oxidation phases), in which case the kids can probably swim. In short, the kids want to swim, and I'm in (for me) uncharted waters with FC>=5!

Brian

you can illute the water sample to get a reading over 5 using your test kit, but it is much less accurate of course. Add one part distilled water (not tap which will have chlorine) to one part pool water. Test and multiply by 2 for estimate of FC level.

CYA binds to some percentage of the available chlorine. What that percentage is depends on the CYA level, high CYA levels bind to higher percentages of the chlorine. If some unbound chlorine gets used up, some currently bound chlorine will be released to maintain a constant percentage bound up.

Without CYA your FC can be eaten rapidly by the sun.

If you want to get into the technical details of chlorine being mostly bound to CYA, then read the "Chlorine / CYA Relationship" section of the Certified Pool Operator (CPO) training -- What is not taught thread. The chemical equilibrium between chlorine and CYA has been known definitively since at least 1974.

Thanks to all for the great input! Here's what I've learned so far, in reverse order this time:

5) All indications are that CH should be climbing for me now, which is a good thing in my case, as my water is really soft (like 150)
4) Sounds like the case of my disappearing CYA every winter is *probably* not the old salt's rumor I heard about CYA congregating on grids even after being dissolved. Sounds like others have seen this mysterious disappearance over winter too, with some having it be just "natural" causes and others due to ammonia nightmares.
3) I'm now convinced that CYA *does* actually do something positive...Jason and ChemGeek's posts were particularly helpful...I especially liked the 1974 study that was referenced in a few places...that did a pretty nice job of describing the mechanism that Jason mentioned...basically, it sounds like the CYA creates a "resevoir" of Chlorine that, while locked up with the CYA isn't very effective, but becomes slowly "unlocked" as needed in order to santize the pool...the level of actual "working" FC in the pool is a result of a pretty complicated equilibrium of all the various Chlorine-related compounds and ions that are in the pool at any given time, and the overall balance also varies heavily with PH (lower = more active FC) and CYA level, such that having *too* much CYA actually becomes a negative, all of which you guys already knew!
2) I definitely need a different FC test! But the dilution idea from Nona is pretty cool, and will help out for now, until I get something better!
1) Until the new test kit arrives, I'm still a tad concerned about whether/when to let the kids in the pool...Of particular interest to me is the situation where the FC level is still high (say >=10), but it's been a while since shocking (say 4 hours at least)...In that case, I'm concerned that long-term exposure to higher FC levels is bad (I've seen some discussions online that talk about tooth decay of competitive swimmers who have prolonged exposure to chlorine), even if oxidation phase reactions from the initial shock application are clearly complete...ideas/thoughts?!? One poster said the rule of thumb around TFP boards is that it's safe to swim with FC<=shock levels?

Competitive swimmers are exposed to far far higher active chlorine levels in indoor pools without CYA than you will ever see in an outdoor pool with CYA in it.

There is no definitive rule about what the highest FC level that is acceptable is. The general consensus is that below shock level is fine, but many people swim over that, The main thing is that you could have FC way above out suggestions and still be way below the HOCl levels that people routinely swim in indoors.