Just to Confirm Before Draining Pool ...

[Noob]

Hi everyone! This site is SO helpful, and I've learned so much already just from lurking; however, I still don't have any confidence, so wanted to pass something by you all. I need to get rid of algae (or what I assume it to be--greenish dust/sediment that moves when disturbed?) and here are my approximate numbers from my K-2006 FAS-DPD (am still learning how to use it, hooray Youtube!):

FC 3.2
PH 8.0
TA 180 (?)
CYA 150-200??? (or so high there's no numbers on the tube!)
CH 600???

Pool Math says I need to swap out about 75% of the water to lower CYA, so I guess that's what I will be doing next weekend, when the temps hopefully come down below 90. After draining and refilling, I then re-test and SLAM based on new numbers, right?

Anything else I should be doing or trying? I don't suppose there's any way to get around the draining/refilling? Lastly, my sta-rite filter cartridges are about 2 years old and have already gone through one heavy bout of algae infestation last summer--do I need to replace them to ensure the algae doesn't come back?

Thank-you in advance so much for reading and for any comments/suggestions!

 

[mknauss]

Welcome to the forum!
You can follow Step 8 in CYA test directions. This will tell you what your CYA if over 100.
Other than that, a drain and refill is most likely the best course of action. Your CH is not bad, just the CYA. As it is supposed to be cloudy and cooler later this week, that would be a good time to drain. Never leave plaster to dry out in the hot sun.
My cartridges are 5 years old and just fine. All they need to be is cleaned. As long as the filter media is not compromised and the end caps are not deteriorated, clean them and reuse them.
I suggest you read ABC's of Pool Water Chemistry and consider reviewing the entire Pool School eBook.