Puck based system and REALLY low CYA


Well-known member
May 23, 2007
Hi Everyone,

This is a bit of a weird one, but wanted to run it by everyone and see what they thought. We have an 18'X40' inground vinyl pool, with an inline chlorinator. We bought the house last fall, and this is our first summer with a pool.

If you see my other threads, we are in Canada, and it is all but impossible to get a decent testing kit for our pool (To get a basic K-2005 is $285 + taxes + delivery). Up until now, i've been using the basic kit to keep everything in range, and finally broke down and bought test stripes just to make sure something wasn't completely out of whack.

This pool is fairly old, and has always been chlorinated by using trichlor pucks according to the owner. When they closed it last fall, they didn't drain much water if any from it (it was actually mid-way on the skimmer).

Keeping all this in mind, I half expected to get high CYA levels using the strips, but I ended up getting the following:

FC: 1-2 ppm
Alk: Normal (60 I think? Going off my memory, but it landed right inbetween the "normal" range listed on the package)
pH: 7.2
CYA: Somewhere between 0 and 30

So the CYA levels really threw me off, which brings me to my question, just how much CYA do pucks add to a pool? It looks like I need to add some, but i'm worried that I'm going to regret that in a bit since I'll be sticking with pucks for the season (BBB looks good, but we're new pool owners, and are frequently out of town 2-3 days at a time).

Anyone have any figures on how much your CYA raised over the season by using pucks?

Also, anyone have any ideas how despite this pool being run on pucks for about 8 years, it has such a low CYA level?

The Mermaid Queen

TFP Expert
LifeTime Supporter
Mar 28, 2007
Northern KY
for each 1ppm Cl, you get .6 ppm CYA from a puck.

Do you have (gasp) a pool store that can test your water? Then you can maybe tell if your strip reading was way off.

Alk is usually suggested a bit higher, like 90-120.

Beyond that I cannot help...

ETA :shock: Amazing, I was wrong again! corrected my error... :roll:


TFP Expert
Platinum Supporter
LifeTime Supporter
May 7, 2007
Silver Spring, MD
Many, but not all, pools lose most or all of their CYA over the winter. It is not that uncommon to open to zero CYA. This is part of why the pucks work at all. If more people held their CYA level over the winter no one would use pucks at all.

With regular trichlor pucks, for each ppm of chlorine you add you are adding 0.6 ppm of CYA. How much CYA you add over the course of a year depends on your rate of chlorine consumption and the length of your swim season. In many pools it can exceed 300 ppm per season, though it is probably lower where you are.

The other problem with pucks is that they are constantly lowering your PH. Your PH is down to 7.2. If you are using pucks you should raise it right away before it gets dangerously low.


Mod Squad
TFP Expert
Apr 4, 2007
SW Indiana
Craig said:
I thouht the only way to reduce CYA was by draining a pool?
A great deal of dilution occurs in some pools over the winter, but it appears that there is some other factor in the complete loss some people experience. There is evidence, at least anecdotal, that biological breakdown occurs in some cases. Maybe algae, maybe something else.