SWG settings, Variable Pump Speed and CYA/FC Target Questions

[Steve-D]

Rather than hijack the "SWG settings and regulating with varying pump speeds" thread I'll post my questions here....
From that thread:

The whole point of CYA is to reduce the amount of FC consumed by the sun. Once your FC is increased, it does not take more chlorine to keep it there.

The higher the CYA the more of the FC is buffered and the less you feel it.
A pool without CYA is much harsher feeling than a pool with CYA.
I run my pool at about 7 ppm of FC. You cannot tell there is any chlorine in the water, no smell, no feel, nothing.

@Jimrahbe - A side note on that thread might be helpful to folks like me who want to better understand SWG output and the recommended/ideal targets for both CYA and FC. I know am much better at following instructions when I know the "why" of things and I'm sure others do, too.

One misconception I've had that you cleared up is that FC output of a SWG is not based on flow/pump RPMs (assuming it is running fast enough to generate any FC), but rather on the % of capacity set for the SWG. That makes sense to me now.

What I still have a hard time wrapping my head around is why CYA is targeted so high for a SWG pool, especially where the "ideal" target is so close to the point at which you would need to drain and refill should a SLAM be required.

• Is the point of CYA @ 70-80 to extend the life of the SWG by virtue of being able to run it at a lower % of capacity once you hit the target FC?
• If the pool is covered (solar cover) for a large part of the day when the pool is not in use does that reduce the need for maintaining the higher CYA level?
• Does the "buffer" from the CYA reduce the risk of dropping below the "minimum" FC target (and thus reduce the risk of an algae outbreak)?

Our old pool was a small (9000 gal) ABG and we had decent city water so partial drains and refills were fairly easy to manage, but now we have a well and a lot more pool water to work with so I am very leery of getting too close to where we would have to drain/refill more than a few inches (2" = approx 600 gallons for my pool). If I had to drain and refill with enough water to get from a CYA of 70 to 40 that probably means trucking in the fill water at a cost of about $500 since the price is per truck load and not per gallon...and that flies in the face of the "keeping costs down" goal of the TFP process.

This is our first in-ground pool and our first season with it so it's a whole new learning experience. We spent more than we had hoped to get the pool in the ground and running so keeping operating costs to a minimum is important. Just as important, however, is operating it at levels that will help to keep the equipment and the plaster in optimal condition long term. Understanding why the various "ideal" levels are what they are will help us to maintain our discipline and to identify where it might be appropriate for us to make minor adjustments to those targets.

 

[Jimrahbe]

Steve,

Is the point of CYA @ 70-80 to extend the life of the SWG by virtue of being able to run it at a lower % of capacity once you hit the target FC?

We are just trying to find a good balance between too much and not enough CYA so that we can run the cell at the lowest output possible. In theory this makes the cell last longer.

If the pool is covered (solar cover) for a large part of the day when the pool is not in use does that reduce the need for maintaining the higher CYA level?

Our recommendations are based upon NOT having an auto-cover. From a practical point of view your auto-cover is just like having high CYA. You should adjust your CYA based upon how much time the cover is opened and closed. You want at least a CYA of 30 to make the chlorine feel less harsh, and because the sun will consume the FC faster with a CYA of 30 vs. 50 or 70. You also need to open the cover let your pool "breath" to get rid of any CC.

Does the "buffer" from the CYA reduce the risk of dropping below the "minimum" FC target (and thus reduce the risk of an algae outbreak)?

I am by far not a chemical expert, but basically the CYA holds FC in reserve so that as the FC is consumed new FC can take its place.

I personally like to run my pool at my FC "Target" or higher. This way I never have to worry about falling off the cliff of doom (Minimum FC). I am not a fan of continually adjusting things, in an effort to stay between my minimum FC and my target FC. That is just too much work for me, with no real gain.

Thanks,

Jim R.

 

[Steve-D]

Thank you, Jim. So the CYA/FC guidance is aiming for putting the least stress on the SWG so it lasts longer balanced against keeping the pool sufficiently disinfected...that makes perfect sense.

We don't have an "auto-cover" but we only remove the <bubble-sheet/plastic> solar cover if we intend to use the pool on any given day, and then only either right before use or with enough lead time to run the Pressure cleaner (Polaris) for an hour or two ahead of our expected swim time. My wife likes the pool warm (83-85) so she wants the cover on to prevent heat loss more than anything else...and for me I don't want to be burning any more propane than I need to in order to keep her happy.

With the house and tree line the pool starts to get sun around 9 AM and sees the last of direct sunlight around 4 PM. If the water temperature ever gets to the point that we choose to leave the cover off overnight the pool might see a full day of UV exposure but that won't be the norm. We had to clear a lot of trees (almost 20) to make an open area for the pool and even with the perimeter pretty well cleared the height of the trees dictates that a lot of airborne debris finds its way into the pool...yet another reason for us to keep it covered when not in use.

We have been consistently seeing a CYA reading of 50 in my testing but I just added some more stabilizer and expect it to settle in at around 60...that sounds like it should be appropriate for the way we use our pool. We've only occasionally seen ANY CC in my daily testing so we're probably OK with the pool's "breathing" needs, too. Now its just a matter of tracking FC loss over time (with and without use) and working out the optimal SWG settings.

Again, THANK YOU for taking the time to share your expertise.

 

[mknauss]

FYI -- A solar cover does not reduce the FC loss due to UV by all that much. It helps, but nothing like a true opaque cover.