Calcium = 650!

[chem geek]

Josh,

Welcome to the forum! I will try and answer your questions for you. If what I say doesn't make sense, then hopefully someone else can help out and make the answers more clear.

You are technically correct that higher calcium increases chances for scaling, but your higher salt (TDS) level decreases these chances and in any event changing the calcium from 300 to 600 does not increase the risk of scaling enough to worry about. In other words, with your numbers you could still operate your pool at 7.5 if you wanted to and not risk scaling. Generally, your pool would start to look cloudy before the scaling occurred in any great amount and you are now far, far away from that situation. So, bottom line, don't worry about scaling.

If you drained and refilled half of your pool water with fill water that has CH of 200, then your original pool water had a CH of 1100! That's awfully high. Do you have any idea how it got that high? Did you ever use Cal-Hypo to add chlorine to your pool, even for shocking (since you have an SWG)? If so, you should avoid using that and use chlorinating liquid or bleach for shocking instead.

Now you said you have seen a lot of scaling around your water line and in the SWG unit, but that was probably before your half drain and refill. With a CH of 1100, you still would not be at risk of scaling unless your pH got up higher, say to 7.6 or so. With an SWG system and with your extra aeration, the pH probably wants to rise a lot so perhaps it did get up high and this combined with the high CH and probably higher TA as well all led to scaling. For example, a CH of 1100, pH of 7.6, and TA of 180 would possibly start to scale.

By the way, what is the TA of your fill water? This will tell me what your original TA was before the half drain and refill.

So now after your half drain and refill, your numbers look good. I assume you have your CYA at 80 because that is what the manufacturer of your SWG recommends and we know that most SWG units require higher CYA to operate efficiently. Your chlorine level is high enough to compensate for CYA's reducing the chlorine's effectiveness.

Now here's an alternative you can try to help lower the amount of acid you need to add. You can follow Ben's Lowering Your Alkalinity procedure to get your TA down to 80 or below (but no lower than 60). With the lower TA, you can definitely safely run your pH higher so can then operate at 7.5 (for a TA of 80) to 7.7 (for a TA of 60) where I'm pretty sure you will find your acid demand significantly lowered. Another thing you can try is to lower the power level on your SWG and increase its "on" time (to keep the same overall chlorine generation amount). The lower power level will give the generated chlorine more of a chance to dissolve into the water instead of outgassing (if the chlorine gas generated by the SWG doesn't dissolve into the water, then the net overall effect is a large rise in pH).

If you try this, let us know if it works (i.e. lowers the amount of acid you need to add). If this works for you, then you can always keep your calcium higher (where it is now) to stay in balance, though as I said before you are now far away from a risk of scaling (or corrosion).

Richard