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Just to wrap up this thread, in case anyone needs a reference in the future... In the end I estimate I did about 100% water exchange (45,000 gal) and was able to drop CYA from 150 to 35. (Much more than I would have predicted.) A few minor hiccups along the way but nothing major: pump...

Yes! I was pretty pleased. I'm going to run another sample from deep end and surface and then likely turn the pump on. I had let the FC get low (about 10.0) and a day with the cover open and the sun on it before starting the exchange resulted in a nice green algae bloom. It's a much milder...

I estimate that I'm about 75% exchanged, drawing from the deep end (9 feet) and adding to the surface of the shallow end. I decided to measure CYA at two points: a. Discharge from the deep end (9 feet down) the CYA is: ~55 b. At the surface of the deep end the CYA is ~50 So there...

Oh, yes, the pool CH and salt was in my original post: CH = 440 and salt = 800. Yes, the benefit of living on a farm is that I have a bit of equipment to handle large(ish) jobs. [Although it seems that I frequently tackle jobs where I wish that I had just a slightly lager...

Yes, somehow I missed putting those in: Fill water CH = 75 and salt <200 (so using 100 as an estimate) So that makes Delta T approximately -3.36 (I know I likely didn't capture all the dissolved solids in the pool). In the end I figure I'm likely still: | DeltaT | < 5.0 so there will be a...

Hello, all. Short question up front: What percent reduction in CYA is reasonable for a given percent of pool water exchange if Delta T is very close to zero? With all the rain that Northern CA has gotten I'm tackling a water exchange to reduce CYA (currently about 150, maybe higher). My fill...

Yes, thanks. This morning (12 hours after last night) showed another 2 ppm loss, just like the night before. I'm not worried about it, I just find it intriguing. I'm not going to add anything, I'll measure again tonight. It's all a learning experience for me.

1930 update: the pool went 12 hours (all day today) with zero FC loss (auto-cover closed all day). Maybe the 2ppm FC loss last night was just the pool settling in. I'll just keep measuring and adding LC as needed.

Great to know, thanks very much.

Got it, thanks much.

Yes, you are correct! My use of the word "waste" was inaccurate in this case. Even though I'm on a farm and our used water does not go into a utility reclamation system, I am a fan of saying "every drop I take out of the ground I put back into the ground." (Of course that is only mostly true...

Great, thanks, ajw22. I was erring a bit on the high FC side as I had to dilute the pool water (1:1) for the CYA test and therefore doubled the error range. I hand't thought about using an SWG with high CYA...your point makes sense. I just need to get comfortable with the salt/corrosion/stone...

Agree that pucks drive up the CYA. The pool co. used them, I've not used them since I took over, but it's only been a few weeks. My initial thought was much like what you state above: stop doing the thing that is making CYA higher. My thought above was that if I'm going to replace 75% of the...

Thank you both, ajw22 and Edge70. I wasn't sure if losing 2 ppm from a starting FC of 20 ppm was acceptable. Given it happened in less than half a day and no UV exposure, I just didn't know, even though the thought had crossed my mind--because the water is crystal clear and no visible algae...

As you may have read, I'm moving from a pool company to managing my pool myself using the TFP method. Background thread on that process here: Moving from PoolCo to DIY I'm about three weeks into doing it myself, and getting a feel for how my pool moves. The pool failed an OCLT last night...

Good stuff, thanks. I went and read the full thread. I'll keep the speed of interference in mind, I usually do the phenol red test fairly quickly--about 10-15 seconds. That might not be fast enough at high shock levels, but seems to be working fine for me over the past few days. I'll likely...

Good to know, thanks. I keep distilled water on hand for projects, so that's easy. Question: Does dilution with distilled water not move the pH of the solution closer to 7.0? Perhaps the answer is: yes, but just not by very much (well within rounding error)...? I do recall that pH is a log...

Ah, good to know. I have a Hanna pH meter that I use for soil pH tests. I'll pull it out and calibrate it and see what it says. Oh, it'll happen, I'm sure! Sharing the joy of the pool makes all the maintenance worth it.

Needsajet: Thanks, once I get the reagents for salt I'll have a measure for that. Kul: Thanks for the welcome, I found and read your post on your RO process. Newdude: Thanks, I'd seen that part of the Wiki, but don't yet have a TDS number. With no pucks in the feeder, I let FC drop to get a...

Thanks for the skinny on CYA degradation and on water exchange. Good stuff. I'd not thought about significant levels of salt in my (non-saltwater) pool. I'll grab some reagents and measure. Waiting for pool water to get colder than source definitely means winter here. Even then it may be a...

Thanks for the reply and the data. How do you think it is that you loose 10 ppm of CYA each month? Solely to degradation? I wonder what components CYA degrades into. Does it require sunshine to degrade? (Our cover stays closed most days.) I'm not questioning, just curious and always...

Thanks! Yes, within minutes after my post I read about the dilution test for CYA. Don't know why I didn't think of that. I have a physics background and lots of lab paraphernalia about my shop. So I pulled out some graduated cylinders and precise on the dilution. I did two tests at a 1:2...

Hello all, I've been around the forums for about 10 years, starting when I had to get my mother-in-law's pool in shape for a house sale back in 2012. I appreciate the wealth of knowledge and experience that you all share. Using all the info and methods that you share I turned what had become...