New to Pool Chemistry

[RamenLover]

Hi folks

Thank you all for those that helped me figure out my pool issues. Little background, I purchased a home, water turned green with CYA over 200. I just completed a water exchange and here are my test results.

Total Chlorine - 5
PH - 7.5
Calcium Hardness - 225
Alkalinity - 130
CYA - 40

According to pool school, my calcium is too low, and alkalinity too high? Is that correct? Any suggestions on what to next?

I have a plaster pool. Chlorinating manually.

Thank you!

 

[Oly]

I would test your fill water first to determine the effects of adding your tap water, test CH and TA only
You can use Pool Math to determine how much calcium chloride you need to add to get you calcium level up in the target range for a plaster pool. If your tap water is high in CH then factor that in as well.
My TA (alkalinity) is high like yours and will drive your pH up. Simply reducing the pH with muriatic acid over time will lower your TA. I'm guessing your fill water is high in TA also.
Keep a close eye on your CSI (calcium saturation index) to fine tune your water chemistry and protect your investment.

 

[Rancho Cost-a-Lotta]

The main factor to consider in pool chemistry for a plaster pool is the Calcium Saturation Index. A higher number leads to calcium deposits and scaling. A lower CSI number leads to plaster etching. Optimally, you want your CSI to be on the slightly negative side, between -0.3 and 0.0. Lower CH, pH, and TA levels result in lower CSI levels. You can run a lower CH level and compensate by keeping pH and TA a bit higher. I ran your numbers in Pool Math using a salt level of 500 ppm and water temp of 63 degrees and got a CSI result of -0.13, right in the correct range for a plaster pool.

As time goes by, CH will rise with evaporation and top-offs. pH will rise and you'll add acid, which will lower the TA. Keep tracking CSI and keep in the slightly negative range by adjusting pH. You can run some numbers on your own in Pool Math to see how changing pH effects the overall CSI level.

 

[duraleigh]

According to pool school, my calcium is too low, and alkalinity too high? Is that correct?

Yeah, but they are both close to OK. I would leave them both alone as the TA will come down naturally and the CH will go up naturally. What is the CH of your fill water?

 

[duraleigh]

The main factor to consider in pool chemistry for a plaster pool is the Calcium Saturation Index

I understand exactly what Mr. Rancho is saying to you and I get why but we should cover the very basics with newbies first. The SINGLE most important parameter for you to control and understand is CHLORINE. You may already have a thorough grasp of the subject but, just to be sure, EVERYTHING else falls FAR below chlorine on the importance scale

 

[RamenLover]

Thanks so much gentlemen.

My fill water TA is 110-120, Calcium Hardness is 125.

Not well versed in chlorine. I know not to use pucks and instead use liquid chlorine. How much I am not yet certain of, but my current chlorine level looks swimmable!

I hope to switch to a salt water system as soon as I get the rest of it figured out.

 

[Rancho Cost-a-Lotta]

Maintain FC levels according to the FC/CYA Levels. With a CYA level 40, your FC target level is between 5-7 ppm. The minimum level is 3 ppm; never allow your FC to drift below this level. Use Pool Math to determine the amount of liquid chlorine/bleach to use given the strength of your liquid. You should test and dose FC daily, at least until you get to know your pool's daily FC loss. At this time of year, you'll probably lose 1-2 ppm daily. As winter approaches, you'll use far less.
ABCs of Pool Water Chemistry