First SLAM - High CYA do I have to drain/refill?

[jasonb81]

Hi Guys,

I'm a new pool owner entering my 2nd pool season (last season hired a company to service it). Things were going well for me this year until we left town for 2 weeks. Upon return I noticed a few very small patches of algae on the steps of my pool and slightly cloudy water in the deep end.

Current test results:
FC 5
CC .5-1, at first my solution appeared to turn from pink to clear, after sitting for a minute it looked more pink. So either .5 or 1, not quite sure.
CYA 120
TA 90
CH 350
PH 7.8

I was planning on biting the bullet and slamming the pool with my high (120) CYA. Looks like i need to bring the FC to 47 via 13 gallons of 10% bleach which I can get for $4/bottle at Home Depot. I was thinking it might take another 13 gallons to complete the SLAM process but not sure. I don't believe I have a bad Algae problem (yet). Estimated cost to eliminate Algae and bring pool back in balance is $100. I'm okay with this as a learning lesson.

Should I lower my PH to 7.2 and then start the SLAM? I won't be damaging my pool or SWG with a SLAM FC of 47 will I?

Long term I need to address the CYA, but was planning on doing this in the fall after swimming season. It takes forever for my pool to heat up due to shade and its just getting warm enough to swim in so not wanting to add 50% cold water.

What are your thoughts? Am I okay to SLAM with 120 CYA if I'm okay with the cost? Or will I be creating other issues?

I'd really appreciate an experts opinion before I double down on my mistake. Thanks so much!

 

[Texas Splash]

I would exchange water first. Not only will it help to lower the SLAM FC level and amount of chlorine required, but should also help to expedite the SLAM Process itself.

 

[jasonb81]

if I didn’t drain to lower CYA, am I going to mess up the pool with a 47 FC? Just curious

 

[Texas Splash]

if I didn’t drain to lower CYA, am I going to mess up the pool with a 47 FC? Just curious

No, but the concern with a CYA that high are two-fold:
1 - Is the CYA only 120 or could it actually be higher? Has diluted CYA test been performed to confirm?
2 - That high an FC level spikes the pH quite a bit. We lover the pH before a SLAM, but an FC that high can complicate testing.

To ensure I'm not missing something else, I'll tag @Donldson for some chemistry lingo.

 

[Flying Tivo]

Test for Salt, it could also be high and needed to drain. It would just be a waste of chlorine if you need to drain after slam. Do it before.

 

[Donldson]

To ensure I'm not missing something else, I'll tag @Donldson for some chemistry lingo.

Need a gif of a gopher popping it's head out of the ground

IMO, if the CYA needs to be addressed eventually and it will make a current issue easier to tackle then there's no good reason to postpone it.

That said, you can perform the SLAM Process if you know your CYA level. If you're sure it's 120 (done via dilution and not just guesstimating) then yes, your FC target is 47 (actually 48, it's 40%). Remember that you'll need to test your FC quite a bit at this level, we're talking 94 drops for every test. I'd also caution carefully against trying to estimate how long a SLAM will go. You perform the process until you pass the three criteria (visible algae means the water is not "clear") and not a specific time. So you need to make sure you have the chlorine to do all of this and the reagents to measure the chlorine.

@Flying Tivo TDS is not a reason to drain water. A salt test is not needed.

 

[jasonb81]

My salt is in spec. CYA is somewhere between 110 and 120 which was tested with the dilution method. I thought I could see the dot at 110, wife didn’t think so. Errored on the side of caution @ 120.

good point about the quantity of reagent. I need to check that I have enough. Thanks for pointing that out.

 

[Rancho Cost-a-Lotta]

While in the "maintain" component of SLAM with high FC levels, you can use a 5 ml sample for testing. Use one level scoop of powder. Multiply the number of drops by 1 to calculate FC level.

 

[jasonb81]

Would it be okay to shut down the valves to my two skimmers and backwash drain 50% of the pool through my main drain? Then refill to achieve 60 CYA?

 

[Major_in_MS]

Would it be okay to shut down the valves to my two skimmers and backwash drain 50%

Yes, if....
.....you have a vinyl liner pool, you must leave at least 6 inches of water in the shallow end to prevent liner problems.
.....you have a gunite or fiberglass pool and your area has a high groundwater table, you should not remove enough water to float your pool.
.....you can be present while draining the pool, if your pump loses prime you will have to shut it off and the increased head may prevent you from getting it flowing again.

If your water has a lot of algae/solids/organic material, then on backwash you will be depositing all that gook on the bottom of your sand and it will just get washed back into your pool when you start filtering again. So when draining, set your multiport valve to drain/waste.


That is actually what I did 5 years ago....

Based on what I learned I decided to go ahead and do a water exchange before my test kit arrived to drop my CYA level. So, on Monday, I closed the valve from my skimmer and began draining the pool. I thought, "I'll really get my sand clean by draining through backwash." After about 2 hours of "Backwashing" my sand I realized (Doh) that I was just filtering all this waste water through my sand from the wrong direction and that when I started filtering my water again all this gunk will wash back into my pool, so I jumped up and switched to drain to waste. I lowered my pool water by 3 feet by 1320 (1:20pm for those of you that don't use military time) and dropped three garden hoses into the pool and switched my pump back to filter. At around 1000 Tuesday morning my pool was full again.

 

[Flying Tivo]

@Flying Tivo TDS is not a reason to drain water. A salt test is not needed.

@Donldson I know its not a reason to drain, but he has a SWG, and if it was(its not) double reason to drain. Just encouraging him to drain.

 

[jasonb81]

@Donldson I know its not a reason to drain, but he has a SWG, and if it was(its not) double reason to drain. Just encouraging him to drain.

Yes, if....
.....you have a vinyl liner pool, you must leave at least 6 inches of water in the shallow end to prevent liner problems.
.....you have a gunite or fiberglass pool and your area has a high groundwater table, you should not remove enough water to float your pool.
.....you can be present while draining the pool, if your pump loses prime you will have to shut it off and the increased head may prevent you from getting it flowing again.

If your water has a lot of algae/solids/organic material, then on backwash you will be depositing all that gook on the bottom of your sand and it will just get washed back into your pool when you start filtering again. So when draining, set your multiport valve to drain/waste.


That is actually what I did 5 years ago....

I am concerned about the amount of rain we've had lately. It's rained for a few days and calling for rain until Monday. Not sure if draining ~ 15,000 out of 30,000 gallons would be enough to pop the pool. Ugh...I'm just not sure what to do. Drain now, wait until next week (algae could get worse), or shock with the high CYA levels.

I have a cartridge filter if it makes a difference regarding the backwash. Have a valve to bypass the filter to waste which is what i thought i could use with the skimmers blocked to drain the pool.

 

[Major_in_MS]

I only have experience with one gunite pool, the one my parents had when I was a teen. That one had a pressure relief valve inside the main drain housing that would pop open and let groundwater into the pool to relieve external pressures on the pool. Do you know if your pool has one of these valves?

A hydrostatic relief valve is located in the deepest part of your pool usually under the main drain cover. The purpose of the hydrostatic relief valve is to relieve the pool of water pressure for those with high water tables.

 

[Texas Splash]

A half drain should not be a problem, but out of caution, you could siphon water from the deep end and let new water fill simultaneously from the shallow. Not as efficient, but over time should help. Just a thought.

As Major noted, a hydrostatic valve would be reassuring as well if present.

 

[Major_in_MS]

How old is your pool? Is the Gunite in good condition, without any cracks or patches. Is the decking around your pool level and stable or loose/shifted? Those would be signs of groundwater damage/problems. Was your pool built with a dry well/sump pump system to remove groundwater? Does your yard hold water for a long time after a rain? Is your yard the lowest yard in your area?

 

[Major_in_MS]

You could use a post hole digger and dig a two foot deep hole in the lowest part of your yard. If the dirt coming out of the bottom of this hole is wet, look back in the hole in a half an hour to see how high the water is in the hole. Of course this won't help if it is actually raining at the time.

 

[Major_in_MS]

Is your pool 20' x 40'? If so, 15,000 gallons is about 2.5 feet of water. I'm thinking that would be pretty safe unless your yard is at the bottom of a natural basin and collects all the rainwater from the area.

 

[jasonb81]

I don’t see where a valve could pop out of the main drain in the attached picture. The pool is elevated about 3’ above the rest of the yard. And the ground is pretty saturated and spongey right now. No clue about the dry well pump setup.

 

[jasonb81]

Is your pool 20' x 40'? If so, 15,000 gallons is about 2.5 feet of water. I'm thinking that would be pretty safe unless your yard is at the bottom of a natural basin and collects all the rainwater from the area.

Yeah 20x40 with it being elevated 3’ above the rest of the yard. How did you calculate 15k water being ~ 2.5’ of water?

 

[Major_in_MS]

Yeah, the hydrostatic relief valve is located in the main drain housing under that cover. You would have to remove the cover to see if the valve is present.

If your pool is 3 feet above the rest of the yard, then I think lowering the water 2.5 feet or so would be no problem. As long as your water level does not drop below the level of the saturated and spongey part of the yard. But, understand, your actions on draining or not draining your pool is completely your decision. I'm not an engineer or any kind of expert in groundwater or construction or anything like that.