Water is beautifully clear. FC is 0...

[Sandrat]

btw, I'm a he, (Mike).

I was using the Pool Calculator.com I had seen that referenced here in other forums. It and the TF Pool Math page are nearly identical, but differ in the recommended shock value. I do note that the shock level on your Pool Math page matches your Chlorine/CYA chart.

I'm going to get started. I can't let it get away from me. I'll drain down the pool first about a foot, then will refill. Then will shock with the calhypo since I have it on hand, then will have some liquid bleach on hand to maintain the FC level. I agree that the CH rise won't be an issue, and should actually help with water balance if it's a little higher.

 

[mikemass]

Sorry I saw "Sandrat" and thought that meant "Sandra T."

anyway....

Based on your "$60 box of 73% CalHypo" comment I am guessing you bought a box of a dozen 16oz bags Power Powder Plus at Leslie's, or equivalent. (It fits the price profile)

If that's the case and you haven't used a single bag yet, you can use all 12 bags (over time) and it would increase your CH levels from 200 to only 228. Heck, you could use almost 50 bags and still not get to dangerous levels.

But being that I am suggesting that you do a small H2O change to get your CYA down a touch anyway, you will start with a lower CH. Lets say you start at 170 and use 12 bags over time. It would eventually look like this:

170 + 28 (192ozs effect on a 26k gallon pool from Pool Math) = 198ppm CH - Perfect for a vinyl pool

Go ahead and use it and just reduce the amount of liquid bleach accordingly.

 

[Texas Splash]

Hi Mike! I do believe lowering that CYA will be in your best interest. Please use the Poolmath calculator (link below) and not the calculator.com one. That was an old product I believe. The one below in my sig and from the home page is correct. As you begin the SLAM, you might find it easier or more predictable to use bleach to hit those FC levels quickly and accurately, but as noted you certainly can use both. In the long run it won't go to waste. You'll use it over the season, but for a SLAM sometimes it can be a bit of a pain. Go with your gut on that one. Let us know if you have any other issues.

 

[Sandrat]

Update

I drained the pool down about a foot to lower the CYA level and have refilled. I'm down to around 50 ppm this morning. I overshot a little for a SWG, but I can work within this zone for now.

I decided last night after lowering and a partial refilling to go ahead and start the shock process. The pool calculator recommended a 28 shock level, or 8+ bags of 73% Cal Hypo. I put in 9

After a couple of hours, I tested the CL using a diluted method, and it only showed a level of 10ppm. I put in the last 3 bags and let it work overnight.

This morning, the FC tests at 0. CC tests at about 1 (something I learned while doing this was that using a diluted method of checking CL can give you a false positive if your pool FC is very low. I found the tap water to test higher than the pool water...)

So I guess I need to hit it again. I see that with a lower CYA, the shock level is also lowered to 20, which requires 770 oz of 8.25% bleach. I'm headed to the store to buy a couple of cases so I won't get below the shock level for too long.

I guess I'm really surprised by the fact that there was no visible algae in the pool. Remember, the water has been clear all this time. (It is a little cloudy today after the shock...) I didn't expect there to be this much in the pool eating up the chlorine.

You guys let me know if you think I've missed something.

Mike

 

[Mr Bruce]

With a SWG you actually want CYA around 80. I don't think the earlier posters caught that. But since you've lowered it anyway, it'll make the SLAM easier.

I would go with the strongest liquid chlorine I could find, which it appears you are. If you lost that much overnight, I would hit it hard and fast until it held, as in measuring and adding to SLAM level every 10-15 minutes. Once it held for 30-60 minutes I'd switch to every 2 hours or so. SLAM level for CYA 50 is 20 Pool School - Chlorine / CYA Chart

 

[Sandrat]

With a SWG you actually want CYA around 80. I don't think the earlier posters caught that. But since you've lowered it anyway, it'll make the SLAM easier.

I would go with the strongest liquid chlorine I could find, which it appears you are. If you lost that much overnight, I would hit it hard and fast until it held, as in measuring and adding to SLAM level every 10-15 minutes. Once it held for 30-60 minutes I'd switch to every 2 hours or so. SLAM level for CYA 50 is 20 Pool School - Chlorine / CYA Chart

Yeah, I started with a CYA that tested to over 90, and I was afraid that it would inhibit the ability to shock. My SWG manufacturer recommends a range of 60 to 75. So I made my best guess as to how much pool water to dump, and, as I said, I overshot the mark a little. But yes, the 50 will help the shock process.

 

[mikemass]

With a SWG you actually want CYA around 80. I don't think the earlier posters caught that. But since you've lowered it anyway, it'll make the SLAM easier.

Yeah, I started with a CYA that tested to over 90, and I was afraid that it would inhibit the ability to shock. My SWG manufacturer recommends a range of 60 to 75. So I made my best guess as to how much pool water to dump, and, as I said, I overshot the mark a little. But yes, the 50 will help the shock process.

Being one of those earlier posters that suggested lowering CYA, I was well aware sandrat had a SWG. The whole purpose was not to bring it to a lower level for the sake of a lower level. It was to make the shock process easier (which sandrat understands as per his post above).

70-80 is good for a SWG, but 90 is getting a little hairy, especially when wanting to "SLAM" which I learned from this fine forum in all my reading. Once sandrat gets pool in check, it will be easier to raise back up if he wishes to maintain SWG levels.

 

[Texas Splash]

Hello Mike! Wow, I'm surprised that only a foot lowered your CYA by that much. I'm not always that good at crunching numbers, but a drop of about 40 ppm from just one foot of water surprises me. Still, you'll be fine. Yeah, the organics tore-up that Cal-Hypo, so it's good you're ready to stock-up on bleach. We've seen many times that the water can be surprisingly tricky by looking clear yet still overwhelming the chlorine. Consistent maintenance of that FC level will take care of that. Good luck!

 

[Sandrat]

Hello Mike! Wow, I'm surprised that only a foot lowered your CYA by that much. I'm not always that good at crunching numbers, but a drop of about 40 ppm from just one foot of water surprises me. Still, you'll be fine. Yeah, the organics tore-up that Cal-Hypo, so it's good you're ready to stock-up on bleach. We've seen many times that the water can be surprisingly tricky by looking clear yet still overwhelming the chlorine. Consistent maintenance of that FC level will take care of that. Good luck!

I was surprised at the CYA drop also, as I had figured that a 1' water drop was less than 25% of the overall pool volume. I thought I'd go from 90 to say, 70 or so. But I have also found that an accurate measure of anything higher than, say 70 CYA is tricky, as it can be difficult to determine when that little black dot finally disappears. Combine that with the fact that the gradients on the scale gets closer as CYA rises, and you have a lot of room for error.