SLAMming and adding water?

Euphonicus

Member
Jun 19, 2017
9
Baltimore, MD
Not sure where to begin... I have an older in-ground pool, vinyl liner (replaced in 2012, currently in good shape, I think). Pool is 45'x22', approximately 25,000 gallons. Filter is a Hayward EC65A DE model. We are located on the East Coast, near Baltimore. Weather has been alternately cool and rainy or moderately warm (70-80), breezy, and low humidity. I realize I may be premature in posting without hard test numbers and I apologize in advance for any breach in forum protocol.

Anyway... I'm losing quite a bit of water. Most of it seems to be evaporation, but not all. I've done the bucket test, and the bucket and pool lose about the same when the pump is not running, perhaps 1/4"-3/8" per day. With the pump running for 8 hours overnight I may lose an additional 1/8". Over the Father's Day weekend I lost about 1.5", give or take. So I suspect a leak in my buried return line but I wonder whether the additional loss when the pump is running could be accounted for by the increased evaporation rate caused by the agitation of the water (may be wishful thinking). For reference, I lost very little water while the pool was covered for the winter, maybe a couple inches, so I doubt I have a leak in my liner. The previous liner DID develop a nickel-sized hole in it and I lost almost all the water in the pool over that winter.

AND I'm losing free chlorine pretty rapidly, too. On Friday afternoon, prior to leaving town for the weekend, I added 9 lbs of shock (In The Swim normal shock, non-stabilized I believe). I did not test with FAS-DPD, just the quicky test strip, and FC was deep purple, indicating 20ppm or so. When I returned late last night the water was crystal clear but by this morning it had turned a bit cloudy and FC was back down to zero on the reagent test strip.

I think I have a handle on the procedure for SLAMming but I wonder whether it will be effective if I'm adding water a couple times a week? Or is that kind of FC loss normal? Thoughts, comments, suggestions? Thanks in advance.
 

Texas Splash

Mod Squad
TFP Expert
LifeTime Supporter
FC loss with algae or during a SLAM Process is expected. One key is to maintain that proper SLAM/Shock value as noted on the [FC/CYA][/FC/CYA]. But the other key here is that there is no way you can do that with test strips. The FAS-DPD must be used to accurately test the FC and maintain it. You should also be using regular bleach to maintain that elevated FC level. Also watch to ensure your CYA didn't drop too low. If you suspect a leak, CYA can disappear to a point your FC doesn't receive good protection form the sun.
 

Euphonicus

Member
Jun 19, 2017
9
Baltimore, MD
Thanks for the response. Tonight I plan to check my CYA and also do an OCLT - with a real FAS-DPD kit, not just the cheapy strips. And I've got 24 gallons of Pool Essentials liquid chlorine on order from Lowe's, so if needed I'll start SLAMming ASAP. Thanks again, I'll post back with some real numbers after I do my testing this evening.
 

Euphonicus

Member
Jun 19, 2017
9
Baltimore, MD
Okay, here are the numbers, tested with a Taylor FAS-DPD kit:

At sunset last night:
CYA: approx. 25
FC: 1.8
CC: 0.2
Did not test PH, TA, or CH

This morning right after sunrise:
CYA: approx. 25
FC: 1.0
CC: 0
PH: 7.2
TA: 60
CH: 220

So looks like a passing grade for the OCLT. CYA, FC, PH, and TA are all a little low. This morning I added a gallon of 10% liquid chlorine, a couple pounds of PH increaser (I know I could just use baking soda but I had the other laying around so I figured I would use it first), and I have a sock of CYA stabilizer dangling in front of the return jet. Not sure a SLAM is indicated at this point but I'll test again this evening and see where we are.
 

tim5055

Mod Squad
TFP Expert
LifeTime Supporter
May 11, 2014
10,413
Franklin, NC
Okay, here are the numbers, tested with a Taylor FAS-DPD kit:

At sunset last night:
CYA: approx. 25
FC: 1.8
CC: 0.2
Did not test PH, TA, or CH

This morning right after sunrise:
CYA: approx. 25
FC: 1.0
CC: 0
PH: 7.2
TA: 60
CH: 220

So looks like a passing grade for the OCLT. CYA, FC, PH, and TA are all a little low. This morning I added a gallon of 10% liquid chlorine, a couple pounds of PH increaser (I know I could just use baking soda but I had the other laying around so I figured I would use it first), and I have a sock of CYA stabilizer dangling in front of the return jet. Not sure a SLAM is indicated at this point but I'll test again this evening and see where we are.
A couple of thoughts and comments-

You are using 25 mL sample for 0.2 ppm accuracy. You can go ahead and use 10 mL sample for 0.5 ppm accuracy. It will save you reagents and is close enough for us.

FC is dangerously low. Always follow the [FC/CYA][/FC/CYA]

The CYA test can not deliver a reading ending in anything other than "0". The tube does not use a linear scale (meaning half way between two numbers would be "5") it uses a logarithmic scale (note the differences between numbers as you move up the tube). Just round up to the next line.

In the future if you have a pH of 7.2 don't even bother adding increaser. pH tends to rise on it's own so there is no need to try to hunt for a perfect number.

TA is fine at 60.

Baking soda adjusts TA, not pH.

If the pool is clear (no visible algae included), no CC and you passed the Overnight Chlorine Loss Test I'd pour an adult beverage and go swimming.
 

Euphonicus

Member
Jun 19, 2017
9
Baltimore, MD
A couple of thoughts and comments-

You are using 25 mL sample for 0.2 ppm accuracy. You can go ahead and use 10 mL sample for 0.5 ppm accuracy. It will save you reagents and is close enough for us.

FC is dangerously low. Always follow the [FC/CYA][/FC/CYA]

The CYA test can not deliver a reading ending in anything other than "0". The tube does not use a linear scale (meaning half way between two numbers would be "5") it uses a logarithmic scale (note the differences between numbers as you move up the tube). Just round up to the next line.

In the future if you have a pH of 7.2 don't even bother adding increaser. pH tends to rise on it's own so there is no need to try to hunt for a perfect number.

TA is fine at 60.

Baking soda adjusts TA, not pH.

If the pool is clear (no visible algae included), no CC and you passed the Overnight Chlorine Loss Test I'd pour an adult beverage and go swimming.
After adding a gallon of the 10% chlorine and letting the pump circulate it for a couple hours, FC now tests at 4.5. CC is still at or near zero (adding the R-0003 did not turn the sample pink but there may have been the barest hint of a color change from totally clear, so small as to leave me guessing whether I was imagining it).

I was guesstimating a bit on the CYA. The true number is somewhere below 30. Filling the comparator tube all the way to the top, the black dot at the bottom was still faintly visible. Hence the CYA sock. I think I'd like to see at least 30 since I'm adding water at least once per week to offset evaporation.

The pool is clear - or would be if I hadn't added a bit of pH increaser. It was sparkling prior to that. And I expect it will clear quickly.

Thanks for the tip on the 10ml vs. 25ml sample, I'll stick to that in the future. In truth I was using some reagent that is due to expire in the next couple months, so I wasn't super concerned about conserving it.

Thanks for the help!
 

Euphonicus

Member
Jun 19, 2017
9
Baltimore, MD
Okay, over the past day I've dissolved most of a sock full of CYA into the pool but am not seeing an appreciable increase in my CYA level - it still tests >30. I'm losing chlorine pretty rapidly during the day. Current test numbers:
CYA: >30
FC: 2.5
CC: 0
pH: 7.4
TA: 70
CH: 210

What should I do? Add more CYA? Wait and see if the numbers change? Try a liquid stabilizer? In The Swim's liquid stabilizer seems to be highly rated but they say it's a salt, not an acid - how would that affect CYA testing?

FYI the pool is crystal clear this morning but I am seeing a bit of grayish residue in the creases and seams of the vinyl liner, I presume this is dead algae? Any advice is appreciated!
 

Texas Splash

Mod Squad
TFP Expert
LifeTime Supporter
You can add a little more stabilizer is you want, but no more than 10 ppm increase worth. That way if you do overshoot to 40, it's not a big deal. We don't want to see your CYA spike to 60 or more at this point in the SLAM. The greyish residue does sound like dead algae. That's great. Time to sweep, brush, and/or vacuum. Increase the FC though. Maintaining is key, so it should be 12 at a minimum during the SLAM until you pass all 3 SLAM criteria. If later you find the CYA to spike closer to 40, then your SLAM FC level would be 16.
Adding CYA:
To increase CYA via granular stabilizer, place the required amount as calculated by the Poolmath calculator into a white sock and place in the poolside skimmer basket. For those concerned about suction flow to the pump, suspending the sock near a return jet or from a floating device will also suffice. Best never to allow undissolved granules to rest directly against the pool surface. Squeeze the sock periodically to help it dissipate. Once dissolved, consider your CYA adjusted to that programmed (target) level. CYA test readings should show a rise in 24-48 hours, however some pools may experience a longer delay to fully register. Best to confirm final CYA in about 5-7 days before adding any more stabilizer/conditioner.