OK.

I don't think your CYA is a problem for the moment. Just stop using trichlor or dichlor, and start using cal hypo or bleach.

If you are still at the same location as when you registered in 2012, the Walmart in Greencastle is stocking it:
https://www.walmart.com/ip/Pool-Esse...iquid/48938023

The only cheaper source of chlorine likely to be available to you is trichlor from Sams Club ($2.10/lb for 90% chlorine . . . but ALSO 50% stabilizer. And yes, those %'s are correct, but no, I'm not going to explain here.)

You'll need to maintain your chlorine level at 5% of your CYA, or around 7 ppm.

Also, you need this: Hach 0.15 ppm - 5 ppm iron test strips That's a direct-to-Hach link. They are available on Amazon, but for TWICE the price.

I suspect you'll find that your pond iron levels are much lower than your house water. Compare pond water with house water BEFORE any softener. Softeners remove iron . . . but pool filling tends to use so much water than the iron 'breaks through'.

If it's as I suspect, you'd be better off filling with the pond, using some sort of semi-permanent arrangement.

BUT . . . if you have a sand filter, AND can purchase and use cal hypo, there's another way.

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Also, you WILL need a Taylor K2006 kit. You are going to have to manage pH and alkalinity better than test strips or dealer testing will allow, and if you use the sand-filter + cal-hypo + my-secret-sauce method of removing iron, you're going to have to monitor calcium levels, as well.

And . . . don't use any more HEDP. Every bit of it turns into ortho-phosphates (AKA algae-food) over time. With PO4 levels of 2 ppm (2,000 ppb) you are ALREADY approaching levels that are associated with uncontrollable mustard algae, once water temperatures rise.

Basically, you need a FULL plan in place, BEFORE you start draining and refilling.

And a final caution: I'm not sure about this, but it SEEMS that once a pool has stained, it is more prone to stain in the future. It might be my imagination, but I don't think so. There are all sorts of chemical reasons why it MIGHT be true, such as tiny remaining bits of iron that give new deposits a 'place to start'. Regardless, this has seemed to be the case on pools I've dealt with.

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