Which is worse - TDS or CYA?

First post - great forum full of lots of good advice!

Just spent an agonizing weekend draining, acid washing, patching, refilling, and balancing my pool. What led to this was my running it on auto-pilot for 6 years with no water changes; finally got my water tested and found a TDS > 3000 and a CYA greater than 1000 (I think that is what he said, but maybe it was 100). Regardless, a lot -- needed to change out the water. Eventually led to nasty purple staining which was the straw that broke the camel's back.

So I'd *really* like to avoid (or at least defer for as long as possible) the pain of big water changes. I've been using the trichlor pucks, which from this forum I now know inexorably raise your CYA. So I'm considering going the bleach route, once I've used tricholor long enough after the water change to get my CYA to ~30 ppm. But if I go to bleach, according to the pool calculator, I'm adding a lot of salt (TDS) with every bottle. That too will build up and force a water change. So question is, which is the lesser of two evils? Go with the trichlor and change water due to CYA, or go with bleach and change due to high TDS?

Pool info: 25k gallon in ground plaster pool with attached spa/waterfall in between. Fresh water 2 days ago - latest numbers from my (non strip!!) test kit:

FC 3
TC 5
CH 70 (need to get this up -- that's the next trip to the store)
CYA <30 (can't measure with test kit)
TA 100
Ph 7.4

Given your current readings, I wouldn't be in a hurry to add things. If you just acid washed, there's a good chance your calcium levels will go up over the next week on their own, as plaster loosened by the acid dissolves or flakes off. Just keep the pH 7.4 or higher and you won't do any damage.

TDS from salt -- which is what you get from bleach -- is no more damaging than salt added to use with SWCG. Also, all forms of chlorine become salt, once they are 'used up'; bleach just contains some excess salt.

High CYA has to be reduced OR managed (per the Best Guess chart), which requires an FAS-DPD kit. Your choice as to which you do. Pool Chlor, of Arizona and California has been deliberately running 10,000's of pools with very high CYA for over 30 years.

What I'm saying is don't sweat it too much - keep your chlorine up with tabs now, though

Get the kit (K2006 - Amazon links in my signature); learn the basic chemistry, and then make your decision. You've got time before either presses on you, and you'll be able to make a decision based on a much clearer understanding of your choices.

Hi ritchieca and welcome to the forum. I think you're worrying about something that isn't going to be an issue for you. People go years and years using bleach without worrying about the salt and without doing a complete water change. My pool is in its 11th season with never draining. Poconos (fellow mod) is on his 14th year. There are many other who have been using bleach in their pools for many years longer than that with no worries about salt building up. In fact, some people (who don't even have a SWCG) deliberately add salt because they like the way the water feels.

Go with bleach. You won't regret it.

Again, welcome. Hope you enjoy being a part of our forum!

Thanks all for the advice!

Um... "FOR SALE: 40 LB BUCKET OF TRICHLOR, BARELY USED AND NOW APPARENTLY WON'T BE USED. CHEAP!!"

:)

Good decision to just go with bleach.

I know you are kidding about selling the trichlor but just in case somebody else is reading your post and doesn't know the rule ---- we don't allow selling of things on the forum. I know that wasn't your intent, but we have so many new members on the forum, I thought maybe this was a good opportunity to let people know our policy just in case they didn't already know.

Happy swimming!

Don't sell your tri-chlor tabs! (yeah, I, too, know you were joking) With your new water and your acid-washed pool you may find your pH always rising. And you KNOW your CYA in new water is low. That's actually the one time when tri-chlor tabs work very, very well. They add lots of acid to counteract the rising pH and they add 6ppm of CYA for every 10ppm of chlorine they add.

But, with your new K-2006 kit, you'll be able to watch your CYA rise and when it hits 30 (or 50 if it's a really hot, sunny summer) you'll know to switch to bleach.

As for the salt in bleach. You have about as much worry from the salt in bleach raising your TDS levels to the "danger zone" as you have from the salt in tears!

I've used liquid chlorine for years. One season, in a mad moment, I tried weighing down my wedding-cake steps with 3 50# bags of solar salt, thinking that algae would be less likely to grow in them than in sand (the still water in wedding-cake steps is the hardest place to keep clear of algae). Well, in a couple of weeks the bags were empty! 150# of salt! So a few weeks later I tested my salt and it had shot up to...1600. just about HALF of what you need for a salt water chlorine generator!

TDS levels are just another nonsense scare tactic pool stores use to convince you to buy their most expensive stuff. I'm not saying it's IMPOSSIBLE to get your TDS levels too high using liquid chlorine (Bleach is LC). I'm saying it's so far outside the realm of experiences here that you might as well consider it impossible. I've not seen a case where TDS was problematically high due to bleach. I've hardly seen a case where TDS was problematically high, period. Just like I haven't seen a case of problem-algae created by phosphates and nitrates.

Carl