Starting SLAM today post ~50% drain. Start process after refill?

linzi618

Active member
May 11, 2017
42
Pflugerville, TX
My pool is in the process of draining to ~50 due to elevated calcium and CYA. My water has been crystal clear but after constant reoccurrence of patches of yellow/brown and some green algae on the walls I want this knocked out. Here are my numbers after my last test last night before we started draining this morning: (all tests performed with SpeedStir)

pH - somewhere between 7.5-7.8 (I have a hard time discerning with the red test)
TC - 2.5ppm
(CC - 0.5)
CH - 700
TA - 130
CYA - north of 100

Ive been diligently scrubbing down the walls of my pool manually for the past 1.5 weeks but obv there isn’t enough FC to keep the algae from coming back due to the CYA level, hence the 50% drain. My plan was to start the SLAM after the pool has been refilled and I retest. Is this correct? I’m admittedly nervous about doing the right thing as I’m new to DIY maintenance after my divorce from Leslie’s a few days ago ?. Pics of my current water/algae situation during drain process...(it’s difficult to pick up the slight algae buildup spots)8F265F27-92E2-44F1-A491-586744462113.jpegA07CB92F-6868-42F4-A97E-C35DDF5F9F59.jpeg .
 

Texas Splash

Mod Squad
TFP Expert
LifeTime Supporter
linzi, once you are done with the drain and filled back up, run a new set of tests. You will be most concerned with pH, FC, and CYA. Lower the pH to about 7.2, then verify the CYA so you know what FC SLAM level to hit based on the FC/CYA Chart. from there, it's all about the SLAM Process. It's good you're hitting it now before things get much hotter. :goodjob:
 

linzi618

Active member
May 11, 2017
42
Pflugerville, TX
linzi, once you are done with the drain and filled back up, run a new set of tests. You will be most concerned with pH, FC, and CYA. Lower the pH to about 7.2, then verify the CYA so you know what FC SLAM level to hit based on the FC/CYA Chart. from there, it's all about the SLAM Process. It's good you're hitting it now before things get much hotter. :goodjob:
Thank you fellow Texan! This is my quarantine project and I agree we need it done now as temps climb!
 
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linzi618

Active member
May 11, 2017
42
Pflugerville, TX
I’m planning to start my SLAM once I get my pool refilled from a 50% drain today....refilling currently. I have a VSP that, for the life of my pool (built in 2017) we’ve been running on a schedule of high speed from 7am-6pm, and low speed from 7pm-6am. So the pump is off for a total of 2 hours a day. Do I need to go into our schedule and cut out the two off hours? Should I run 24/7 at low speed or high? Our pool is a free form that seems to have an issue of fine particulate/crane flies gathering in one area no matter the speed we run our pump (in regard to the above comment of running at an RPM to achieve skimming of surface).
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
33,810
Laughlin, NV
We like to see a pump run 24 hours per day during a SLAM, but a couple hours off will not be that disruptive.

No real need to run the pump at a high rpm as long as the slow rpm skims the pool surface. When you are using pucks for chlorination, then the high rpm is needed to properly erode the pucks and add chlorine and CYA to the pool.
 
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linzi618

Active member
May 11, 2017
42
Pflugerville, TX
Thank you fellow Texan! This is my quarantine project and I agree we need it done now as temps climb!
linzi, once you are done with the drain and filled back up, run a new set of tests. You will be most concerned with pH, FC, and CYA. Lower the pH to about 7.2, then verify the CYA so you know what FC SLAM level to hit based on the FC/CYA Chart. from there, it's all about the SLAM Process. It's good you're hitting it now before things get much hotter. :goodjob:
Hi Splash...I made another post this morning. After draining 50% of my pool and refilling my CYA is still 120. I’m stunned. I’ve gotten advice to drain 80+% of my pool again and try again. Since you’re a Central Texan, I was wondering if you could advise whether it is safe for me to drain to near empty vs doing an exchange. We are going to get rain today up here in the Greater Austin area and I don’t want to risk my pool lifting...
 

Texas Splash

Mod Squad
TFP Expert
LifeTime Supporter
I was wondering if you could advise whether it is safe for me to drain to near empty vs doing an exchange.
That is a really tough call. While we're not too far apart, our grounds may be worlds apart. Even here in S.A. if you're on one side of the highway it's clay, but the other pure rock. You might be able to get some info from your County office, maybe Environmental perhaps? Or contact the builder if you can.

Your CYA must've really been through the roof, Good thing you're addressing it now before the heat gets us.
 

linzi618

Active member
May 11, 2017
42
Pflugerville, TX
That is a really tough call. While we're not too far apart, our grounds may be worlds apart. Even here in S.A. if you're on one side of the highway it's clay, but the other pure rock. You might be able to get some info from your County office, maybe Environmental perhaps? Or contact the builder if you can.

Your CYA must've really been through the roof, Good thing you're addressing it now before the heat gets us.
I’m east of 35 (just east of 130, south of 45) in Pflugerville. The storms are just now hitting us. Given how high the CYA is I’m concerned doing the “exchange” method is going to not bring it down enough. Our submersible pump drained our pool 50% in 3 hours and it took our filler plus an additional hose 12 hours to refill so it wouldn’t keep up with the drain rate. I’m tempted to contact my pool builder (A&S).
 

linzi618

Active member
May 11, 2017
42
Pflugerville, TX
That is a really tough call. While we're not too far apart, our grounds may be worlds apart. Even here in S.A. if you're on one side of the highway it's clay, but the other pure rock. You might be able to get some info from your County office, maybe Environmental perhaps? Or contact the builder if you can.

Your CYA must've really been through the roof, Good thing you're addressing it now before the heat gets us.
I’ll add...we are in the shrink/swell (as opposed to rocky West Austin) area but we have a sprinkler system we use consistently so I’m not *terribly* concerned about the ground moving much with this rain, especially since it hasn’t been super hot yet this year. I’m going through my builder paperwork to see what may or may not void my shell warranty...
 

linzi618

Active member
May 11, 2017
42
Pflugerville, TX
Does your pool have a main drain with a hydro-static valve to release pressure from below? That may be something to look for as well.
I’m not certain...I’m looking at the draft plans from the pool construction and I see where it lists main drain but not hydrostatic valve...still close lightning outside so I’m not going out to inspect quite yet!
 

linzi618

Active member
May 11, 2017
42
Pflugerville, TX
First is the shell popping out of the ground. If you have a high water table (near a river, lake, lots of rain, etc) that can happen. It is catastrophic.
There is risk to the plaster. As it dries it can crack, pop off the shell, etc. This is of more concern in the summer and/or the sun shining on the plaster directly.

If any of these are a concern to you, we have methods to exchange the water.
See Draining - Further Reading
I read the water exchange directions and ive got questions regarding knowing the end point. I’m in a similar situation (and geographic locale as OP of this thread). I did a ~50% drain of my pool and refill yesterday and my CYA is still over 100 (120 according to the dilute/x2 method). I’m paranoid about my pool lifting out of the ground by draining too much. But I don’t want to drain 50 and refill 50 only to have my CYA drop only slightly below 100 again. Im in central Texas built in Clay, pool built in 2017 when Hurricane Harvey hit the gulf coast and decimated Houston. We just got a ton of rain in our area but another pool being built in our neighborhood at the same time as us actually DID lift during construction due to all the rain. We are getting a soaking rain today, too.

If I choose to do the exchange method, do I just keep it going and keep testing CYA until I get it to the level I need? I used a submersible pump yesterday and drained 50% in 3 hours but it took 12 hours to refill so I’m not going to be able to use the submersible since my refill flow rate is 4x slower. That was with both the pool filler running and another hose going into the pool.
 

tillmac62

Well-known member
Sep 30, 2019
73
Gaffney, SC, United States
You can still use the pump. Just turn it on and off as needed. The more you drain before refilling, the more efficient the refill will be. Remember, you're doing a dilution. Drain and refill is more efficient than the continuous exchange method. You'll use less water to achieve a given CYA level by removing the water first.
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
33,810
Laughlin, NV
You need a low power sub pump for the exchange method. It is not a dilution. It is based on the two waters being different, in temperature and /or CH and Salt content.
The description on how to measure the rate of water exchange is in the article.
 

linzi618

Active member
May 11, 2017
42
Pflugerville, TX
You need a low power sub pump for the exchange method. It is not a dilution. It is based on the two waters being different, in temperature and /or CH and Salt content.
The description on how to measure the rate of water exchange is in the article.
The only difference between the two waters (pool and fill) at this point is going to be CH. Post refill yesterday my pool CH dropped to 500 from 700 and my fill water CH is 200. It is in the 70s outside right now and raining, pool water is in the 70s, and I’d have to check my fill water temp.

I’m guessing at this point my best course of action is going to be another 50% drain and refill. I’m way too paranoid about my pool popping out of the ground to go much lower, and then doing it yet again tomorrow if necessary.
 

linzi618

Active member
May 11, 2017
42
Pflugerville, TX
Just got off the phone with my pool builder’s maintenance/start-up guy. He re-assured me that I can safely drain my pool completely. I discussed the chemistry parameters with him and given my current CYA level he suggested about a 75% drain. Moving forward with the re-drain with less stress now.
 

linzi618

Active member
May 11, 2017
42
Pflugerville, TX
Hi all,

After a 50% drain and refill with ensuing CYA levels still 120, hub and I drained our pool 95ish% (still about 12 inches of water in our 7’ deep end and 6 person spa still full. Finally filled around 11 last night. Got up this morning and these were my test results:

pH - 7.8
FC - 0.5 (barely turned pink)
CC - 1.5
CH - 225 ppm
TA - 160
CYA - Less than 20 (hallelujah, but...)

I spoke with the pool builder maintenance guy who did our startup in 2017 who gave us the go ahead to drain to at least 75%. He told me to continue using pucks in my chlorinator, but only use up to 3 and keep the flow rate low, and expect to do *some* draining every couple of years to mitigate the CYA buildup.

So now I’m back at getting my pool to swim able (I’m in Central TX so we never “close” our pool). I just added three pucks with a flow of 2 into the chlorinator because with little to no CYA presently in the pool I don’t think I can start with my bleach/shock process. We just added 76 ounces of MA (20 Baume) to lower the pH as per the pool school app. I’m babysitting this copiously so I’ll test (with speedstir) often.

Question - can I expect my chlorinator/pucks to raise my CYA to suggested level somewhat quickly? Not sure what to expect as this is my first time “starting over”. I know I need to be around 30. Am I looking at having to get CYA increaser so I can get the ball rolling with SLAM? (My initial reason for starting this whole process was a mustard algae problem on just the walls, water was crystal clear, and incorrect CYA readings from Leslies. My plan had been to drain to drop the CYA to suggested levels then slam.)

Advice appreciated!
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
21,122
Northern NJ
Pool Size
35000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
I just added three pucks with a flow of 2 into the chlorinator because with little to no CYA presently in the pool I don’t think I can start with my bleach/shock process.
You can begin your SLAM Process now. Lower your pH and begin by adding 12 ppm of liquid chlorine ASAP.

Question - can I expect my chlorinator/pucks to raise my CYA to suggested level somewhat quickly? Not sure what to expect as this is my first time “starting over”. I know I need to be around 30.
Every 8 oz Trichlor puck will add 2.7 ppm or FC and 1.7 ppm of CYA and lower pH by 0.15 to your 20,000 gallon pool.

It will take 10 tablets or so to get you around CYA 30.