Advantage of higher CYA levels when using SWCG?

[dooger54]

Just did a complete drain/refill of my pool. For now my CYA is only 40 and I am hesitant to increase it anymore. I know the only way to decrease CYA when it gets to 90-100 is to drain water and I don’t want to have to do that again anytime soon! What is wrong with leaving it at 40 instead of the recommended 70?

By the way, I just ordered my SWCG and will be installing it this weekend.

 

[PoolStored]

Despite what a great deal of the available literature says, higher CYA levels reduce the total amount of chlorine required to sanitize your pool. Even though a higher CYA level requires a higher FC level, the amount of chlorine you need to add each day to maintain that higher FC level is actually lower than what you would need at a lower CYA and FC level. This happens because CYA protects FC from sunlight, reducing the amount lost to sunlight enough to more than make up for the higher FC levels required.

Since less total chlorine is required at higher CYA levels, the SWG cell doesn't need to run as long each day. Since the cell in a SWG has a lifetime based primarily on how long it is on, a lower daily run time results in longer cell life.

 

[AK-]

There is also the fact you are slowly adding chlorine over time rather dosing LC once a day, that avoid the chlorine spike. The higher the FC the higher the FC loss… Also the SWG will most likely prevent you from ever having a FC too low (unless you lose power or intentionally turn the system off).

 

[AK-]

higher CYA levels reduce the total amount of chlorine required to sanitize your pool

I believe what you meant to say is it reduced the amount of chlorine you need to add to keep your FC level (because it reduces chlorine loss).

 

[dooger54]

Ok, very helpful. I wondered how you are using less chlorine when a higher CYA level requires higher FC. This explains that, thank you!

If I increase to 70 how long might it take for the CYA to cling back to 90 or 100 and I am forced to drain again? It cost me about $1300 to refill my pool last month so I’m skittish about CYA levels!

 

[AK-]

Ok, very helpful. I wondered how you are using less chlorine when a higher CYA level requires higher FC. This explains that, thank you!

If I increase to 70 how long might it take for the CYA to cling back to 90 or 100 and I am forced to drain again? It cost me about $1300 to refill my pool last month so I’m skittish about CYA levels!

As long as you don’t intentionally add stabilizer and don’t use Trichlor/Dichlor tablets/pucks it won’t cling up. CYA actually degrades over time… about 1-4ppm per month. Funny thing is higher FC faster CYA degrades (it is still way too slow to avoid draining a high CYA pool).

 

[nobody291]

What is wrong with leaving it at 40 instead of the recommended 70?

Nothing is wrong with running your CYA at whatever level you like. But, if you want to minimize the amount of FC your SWCG needs to generate each day, CYA of 70-80 is the way to go. I have a SWCG that is much larger than what my pool requires, so I've brought the CYA to 50 for the summer and am going to try to run it there. I like the idea that if there's a power outage or a CB trips while we're away, we will be able to SLAM more easily at a CYA of 50, even if that means we're running the SWCG 5 or 10% higher.