High CYA (with SWG) - Replace water or not?

[Dagobah]

All the details of my last few weeks here: big-swg-pool-with-algae-shocking-with-clor-brite-t63355.html

Current Results:

FC 15
CYA 90-100
TA 150
pH 7.8

What I've done so far:

• 
  Reduced my SWG run time. Planning on reducing even more until FC gets to 6.
  Added muriatic acid once (pH was higher). Planning on continuing to test and add acid to bring it down to 7.2.
  Started aerating for 8 hours a day with my fountains to reduce TA

It's been suggested that I should replace my water to reduce CYA levels. However the pool calc indicates I'd need to replace up to 25% of my water. I've never done this before. What other complications would come with doing a partial replacement? I've also got a pool party coming up this weekend... better to just wait until after and re-test and then decide what to do?

 

[Bama Rambler]

I'd go ahead and drain 25% of it now and refill it. You'll probably need to add a little salt but it should be easy to rebalance before the party. If you do want to wait till after the party, that's fine, but I'd raise the FC to the top normal range for 100 ppm CYA.

 

[Dagobah]

Sounds good.

Next question, how do you estimate 25% ? I have one side that is at diving depth, other much less. And volume being rather deceiving to eyeball.... Is there a better way than guestimating when I've hit 25% while dumping water?

 

[Bama Rambler]

Basically just guess at it. If you figure about 1/3rd the way down the shallow end would be about 25% of the total.

 

[Dagobah]

Replaced 25% of the water last night. Checked it about an hour ago, and CYA has come down within range!

FC 7.5
pH 7.8
TA 150
CH 200
CYA 60-70

Now just need to get my pH and TA in check, and monitor my FC levels while I dial in the new SWG. I'll also be checking my salt level later on today.

 

[Bama Rambler]

See, that wasn't bad at all.

I'd raise the FC a couple of ppm with bleach just before the big party this weekend.

 

[Dagobah]

Yea, had to figure out how to select only my main drain (and not the skimmers), but was just trial and error.

Once I get my pH and TA within reason, think I'll try adding borates next. Just need to figure the most cost effective way first.