SLAM Now...or Wait?

[mld213]

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.

My current question: Do I SLAM now or do I wait?

Background: CYA is 160 so I have been targeting FC = 20 using LC 10%.

It *seemed* like I was having to add a lot of LC (1 gal a day, sometimes 2 gal a day). This seemed particularly high given that the safety cover stays closed most all of the time (and I assume that no UV is getting through the cover).

So I did an OCLT. Measured FC last night after dark at 2200 and then measured it again this morning at 0730 when foggy before any light on the pool. I’d lost exactly 2.0 ppm FC. No sunlight loss because it was night, and on top of that the cover was closed. CC = 0.

So there is a biological load that is consuming that FC (2.0 ppm in 9.5 hours); organic matter or algae or something else. I just don’t see it anywhere: water is crystal clear; no cloudiness when I brush the walls; nothing stirs up when the sweep runs; steps are clear; no ladder or water features for algae to hide in. Maybe there's something behind the lights in the niches?

We are supposed to get an inch of rain this weekend and I’m going to drain an inch from the pool before the rain and use that rain to dilute CYA.

So, I was thinking I'm not going to SLAM the pool now, b/c it will just get diluted.

Thoughts?

 

[ajw22]

I am not sure losing FC or 2 from a CYA of 20 is a fail for the Overnight Chlorine Loss Test. High FC levels like that naturally lose FC.

If you lost FC of 2 starting from a FC of 7 that would be a fail. Losing 2 from 20 may be fine.

You cannot do the SLAM Process with a CYA of 160. Your SLAM FC would be around 64 which you can't maintain even if you can get to.

I doubt your inch of rain will lower your CYA much.

At this point I would not worry about your OCLT loss.

How does your water look?

 

[Edge70]

With CYA of 160 it's going to take a lot more than draining an inch of water and some rain to bring it down much. With a CYA of 160, you'd have to drain and replace half the water in your pool to get to a CYA of 80 which is still on the high side for a pool that's not salt water. I understand where you are at as I was there a couple years ago. It's a pain to fix but it can be done with some time. Somewhere around 40-50 would be much easier to manage. I'd focus on getting this CYA dialed into a range first and then you can look at slamming later if need be. Your water is clear right now which is great so no need to panic. Your losing a bit of FC but it's not a crazy amount. Like ajw22 said, a SLAM is pretty much out of the question right now until you get CYA under control.

 

[mld213]

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. I also wondered--if such a loss is normal/acceptable--why it is the case. Perhaps it's just naturally hard to hold that high of an FC level.

Agree that an inch of water won't affect CYA in a measurable way. I'm just hoping to dilute slowly over the winter instead of doing a large drain/refill right now given the drought conditions in my area. Even if we have a wildly wet winter and I can harvest a lot of rainfall, there will still need to be some water taken from the water agency; we just don't get anywhere near enough rainfall (at least we haven't in many years). The cost is not a lot, it's a desire to avoid waste during a period of scarcity. A Scout is thrifty.

Or I could just stick a pin on the calendar and say "I'm going to replace 75% of the water on January 15" (or some arbitrary winter date). If that's the case, it likely wouldn't matter if I went back to pucks until that date. I don't mind handling LC, but at 2 gallons a day it is more work than pucks in the feeder. (And pH is creeping up, but still in bounds at 7.8). By my calculation, pucks are a bit more expensive than LC.

For my 45,000 gallon pool:
40 lbs pucks for $190 give me $1.96/ppm FC increase
2 gal LC for $8.00 give me $1.84/ppm FC increase

Doing a single replacement would also allow me to move to a salt water pool at that time as well. Although, I was considering moving to salt water sooner to see if I liked it; if I didn't, there was the option to going back to fresh at the drain/refill. The only concern we have with salt is that we have bluestone decking; I've read a number of posts from people who have concerns, but I seem to have also read a number of posts from people who have not had problems--all anecdotal to me at this point so I figured I'd try it and see what happens. I doubt it will be a problem because we have so little spash-out.

 

[ajw22]

Your CYA will naturally degrade some over the winter.

As long as you do not lose control of your water chemistry and let algae take hold you can continue to chlorinate using liquid chlorine at around 12- 16 ppm. FC should be 7.5% - 10% of CYA level.

I would not go back to pucks.

You can put in a SWG anytime. The SWG will work fine with CYA 160. Putting in the SWG will save you the hassles of all the chlorine jugs.

If you don;t let algae take hold you can manage your water chemistry and get through until your CYA naturally declines to more reasonable levels.

 

[Edge70]

Your use of pucks is what's contributing to driving up the CYA numbers. If you want to work on getting this lowered, you are going to have to stop using these and move to LC for the time being. Handling of LC is a pain, no question. So long term, you can look at switching to a SWCG or get a more automated way of dosing LC to your pool. I installed a Stenner pump on my pool this year and the maintenance is very minimal. Along with the pump, I added a 20 gal tank that I fill with LC once a month. I test the water a couple times a week now and maybe have to add a little muriatic acid to keep PH in line. That's really it. I would have installed a SWCG but availability was super scarce and I have an autocover on my pool and I was a little concerned that the salt wouldn't play nice with the aluminum tracks on my pool deck. Agreed that pucks are more convenient than LC but once you understand how they drive up CYA and prevent your FC from being as effective as it can, you won't want to use them anymore.

 

[mld213]

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 water in four months time, the little bit of CYA that pucks would add over those four months would not make a difference in the end. That stated, I fully realize that use of pucks is incompatible with the TFP method. And, they are a bit more expensive.

Maybe I could slowly let me FC drop and see where I start to notice clarity degradation. Instead of targeting 20 ppm, maybe I target 18 or 16 ppm, week by week. I just don't want to walk so close to the edge that I fall off, thus my targeting 20 ppm (12.5% of CYA).

I also have an auto-cover, and aluminum tracks, pulleys, cover bar, and bar that the cover rolls onto. I've read that one can rinse them once a month (or more often) with fresh water to reduce corrosion, but that's just not likely to happen in my case. The bluestone slabs over the cover-box come off once a year to sweep leaves out. They are heavy; it's not realistically a monthly job. I'll search the forums for threads on salt water and auto-covers.

A Stenner pump is an interesting idea, thanks for mentioning it. Do you fill your 20 gal tank with 1 gal jugs of LC?

Thanks for the conversation.

 

[mld213]

FC should be 7.5% - 10% of CYA level.

I would not go back to pucks.

You can put in a SWG anytime. The SWG will work fine with CYA 160.

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 aspect.

The good news is that the pool sparkles and is perfectly swimmable, so no reason to do anything dramatic right now. Control variables; incremental changes; measure; adjust.

 

[ajw22]

When you see clarity degradation it means you have algae and it is too late. Do not let your pool get to that place.

12.5% of CYA is ok. High FC is better for you then low FC.

 

[mknauss]

If the cost of the water is reasonable, drain and refill to lower the CYA. The water you put into the Water Reclamation system is not 'wasted'. Nearly all of it is returned to the water system in your area.

 

[mld213]

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 as there is a small amount that evaporates and thus does not end up in the ground.) Every drop is reclaimed and most all of it goes right back into the very watershed it came from (except the small amount that evaporates and precipitates elsewhere). Before I put it back in the ground it waters crops and animals and facilitates life, so it is definitely not wasted.

 

[mgtfp]

I wasn't sure if losing 2 ppm from a starting FC of 20 ppm was acceptable.

It's bit of a grey area there. One of the expected chlorine losses (without algae) is from chlorine oxidizing CYA. The loss from that is kind of a percentage of both, FC and CYA level, and also higher at higher water temperatures.

The OCLT pass criteria are designed to cover typical TFP FC and CYA ranges.

 

[mld213]

Got it, thanks much.

 

[Edge70]

A Stenner pump is an interesting idea, thanks for mentioning it. Do you fill your 20 gal tank with 1 gal jugs of LC?

Normally I buy my LC in bulk from the local pool company. I still find they are the cheapest place to get it. I use 10L containers meant to hold the chlorine. I also have 20L containers but I find the 10L ones easier to lug around when time comes to refill. I have a small pump that I use to transfer the LC into my holding tank. It only takes a few minutes and minimizes splashing from trying to pour it in. I only have to do this every 4-5 weeks so it's not a huge deal. Compared to what I was doing this is very manageable and barely any effort at all. Also, with the autocover, since the pool isn't exposed to sunshine all day (UV ), the pool doesn't lose much chlorine at all once you have the pool levels dialed in. I find I have very little chlorine loss so I really don't have to add much chlorine. I'd highly recommend this or convert to a salt water system...

 

[mld213]

Great to know, thanks very much.

 

[mld213]

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.

 

[Edge70]

1930 update: the pool went 12 hours (all day today) with zero FC loss (auto-cover closed all day).

Well that's a positive sign and should make you feel better. Now, you can focus on that CYA on your own terms.

 

[mld213]

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.