New CYA guidelines and FC levels

[jacojudy]

I'm a new pool owner (vinyl liner, 25K gallons) with almost no experience maintaining water quality. Pool school was very helpfull but when talking to local (Jacksonville FLorida) professionals there seems to be a lot of difference of opinion concerning CYA levels.
3 Locals state that at a recent pool conference, higher CYA levels (around 100-120) are completely acceptable and are no cause for concern.
How will this affect the FC guidelines stated on the FC/CYA table if at all?
Initial readings on my pool were as follows:
FC - 5
CYA - 120
Total Alkalinity - 100
pH - 7.6
Total hardness - 100

These are all in the acceptable ranges, however the pool water has significant algae growth. I'm assuming that the high CYA level is limiting the effectiveness of the FC.
On the advice of the locals, I shocked the pool with 12% NA Hypochlorite purchased from them. 3 days later the pool finally cleared up, was brushed and vacuumed.
Now the FC levels are >10 and I was told that we should NOT swim in the pool with FC values >10.
I'm confused by this after looking at the FC/CYA guidelines on this site where at a CYA level of 100, the "Target" FC level is 12.
Are there posted levels available at which you should NOT use your pool? If so, where are they?

 

[Ohm_Boy]

Unfortunately, what we know about CYA and its relationship to chlorine hasn't really found it's place in the mainstream just yet. However, the reason you have algae with levels in "acceptable ranges" is because the ranges aren't really acceptable. CYA buffers FC, and while the chemical/water/pool companies will tell you that, they don't know/care/say that the effectiveness of the FC is also diminished by the CYA. Thus, higher FC levels in the presence of CYA are equivalent to much lower levels with little or no CYA. There is a chart in Pool School that reflects how this relationship works and indicates good levels of FC for given levels of CYA.
We've seen this challenged for years by mainstream water quality guys, both here and on other pool forum sites, but our information is borne out by real-world experience.

Sorry to say it like this, but you'll have to either listen to us and get your water safe, clear and sanitary, or you can listen to others and have algae, scale, and bacteria and/or spend way too much on chemicals and water.

 

[mikespoolfl]

I have to agree with Ohm_Boy. Since lowering my CYA from 90 to 40 by lowing and refilling and following the advice on here I've not had any problems with algae or cloudy water. If you try to mix and use advice from different sites it won't work. This is a tried and true method.

 

[duraleigh]

3 Locals state that at a recent pool conference, higher CYA levels (around 100-120) are completely acceptable and are no cause for concern.

Shortly and Bluntly put, they are all three simultaneously incorrect!! :lol:

 

[jacojudy]

In defense of the Locals (why I'm not sure), 2 of 3 did say it would be best to lower the CYA level using the drain /refill procedure and then follow essentially the same guidelines posted on TFP.
I'm still confused about the FC/CYA relationship and levels needed for me to safely take a swim.
Is a level of 8 acceptable (not dangerous) in a pool with a 120 CYA until I can get the CYA level down to the 50-80 range?

 

[XsAllOverIt]

A level of 8 is safe with any level of CYA. As long as you don't exceed shock level, you can swim in the pool.

 

[Ohm_Boy]

Honestly, you can swim in FC > 20 with CYA=120.

You can safely swim in up to the specified shock levels for your CYA, and obviously, we swim in the target levels all the time.
Refer to the CYA/FC Chart

 

[jacojudy]

Thanks for the info about FC/CYA and swimming. I drained about a foot of water yesterday and refilled.
I have a well and am trying to spread the drain/refill process accross more than one electric bill if possible.
My pool is finally clear (no algae) and looks real inviting.