Can't keep my FC

[jokerfive]

Long time listener, first time poster. This site is amazing by the way, kudos to all of you and thanks for the wealth of information to a newbie pool owner. We installed a new gunite pool last year (water filled beginning of August) and, since then, I've been diligently testing with a TF-100 test kit, ignoring pool store advice (although they "need to test" for my plaster warranty) and educating them that they don't understand what's in the "other 80%" of the stuff they sell. It's been a fun year.

Ok, more importantly, we have a 23,500 gallon pool with an auto safety cover. In the fall, I found that my FC would easily creep up if the pool stayed closed for even a day or two. So I routinely would find FC creeping above 5.0ppm and would lower the SWG % down from my 50% setpoint, to 10-20%. I noticed CC could also get to 0.5ppm but a nice day of sun with the cover open would clear that up easily.

This spring has been quite a different story. I feel like I can't keep FC in my pool, and have had to subsidize the Cl levels with gallons of bleach (I've probably used 5 gallons over the last 3 weeks). I did an overnight FC loss test about a week ago, and I lost 0.5ppm.

One strong theory I have is that there is a lot of pollen, seed pods, etc falling in the pool. I have skimmer socks on and replace them every couple of days. However, when the cover is open it's also usually sunny. Also want to make sure it's not something else or you all might have some other recommendation.

Current SWG setting is 75%, with the pump running 12 hours per day (7a-7p). Water test with TF-100 is below.
pH 7.6
FC 3.5
CC 0.0
TA 100
CH 275
CYA 65
Salt 3300
Borates 30
Temp 79F
CSI -0.21

I just added some CYA, after this test, to pull that up a bit into the "ideal range". This morning I tested the FC at 4.0 when I opened the cover, so lost about 0.5 during the day today -- again, can't tell if this is sun or the junk falling into the pool. I'm just surprised I can't maintain the levels even with the SWG running so much higher than I've ever had it. Yesterday I added a gallon bleach to bring the FC up to 5.0 (before people went in the pool).... again SWG running @ 75% and I was at 4.0 this morning.

Btw, I did just do a SWG inspection as the OmniLogic timer went off. It was clean and looked brand new. Any other thoughts? Am I just being paranoid and should run my pump longer/at a higher setting/add bleach and this is mostly normal?

 

[YippeeSkippy]

Hiya Joker Welcome aboard the SS TFP.

Let me get this straight- plaster pool, right?
SWG- but what size?? Is it undersized??
CYA is now 70 or 80 - Your FC is low for this.
Your CSI is good
That was water temp I take it, the 79 degrees??

Did you raise your FC level to the desired level with liquid chlorine before turning the SWG on? The device works too slowly to take you up from zero (which I am assuming your pool was when it opened??).

How often are you opening/shutting the cover?

If you could please go to <Settings> and find the <Signature Line> option and fill it out with details about your pool, size, finish, equipment in use, how you chlorinate and test, yada yada yada, it would really help us answer better. Thanks in advance

Maddie

 

[Msch99]

CYA of 65 counts as 70. 5 FC is absolutely minimum, target 8-10. I would do an OCLT to see if have start of algae bloom

 

[YippeeSkippy]

He did the OCLT already and only lost 0.5ppm.

 

[Msch99]

He did the OCLT already and only lost 0.5ppm.

Blind one eye can’t see out of the other! Sigh

 

[YippeeSkippy]

Well you were spot on about the CYA/FC level suggestion!

 

[jokerfive]

Sorry, will update signature line. Thought I already did that and it’s in my profile. Definitely not an undersized SWG, as I have the Hayward T-15, and it also was plenty in the fall for about 3 months of operation.

I did open with bleach and did a SLAM. The above is just maintaining FC. I opened 7 weeks ago, so it’s not really having to do with an “open”.

I hear you on FC/CYA ratio. However, if I understand that ratio correctly, the higher my CYA the less effective my FC becomes (so it has to be higher). My problem here is that I’m losing FC. So if I took it up to 8ppm I think I’d still lose FC at the same ratio (it just now would be a better sanitizer if I was at 5ppm). Or are you saying there could be an algae bloom I haven’t destroyed yet because I haven’t gone high enough on FC... so 5.0 is still “low” for my CYA and something’s hiding out on me.

 

[OHcabanaboy]

Double check your CC. You've got something more than sun eating chlorine IMO.

 

[jokerfive]

CC has definitely never been above 0.5 (DPD-FAS test - CC part is either clear to begin with or takes one drop to take it to clear). But again my cover would generally be open and sunny. So I could be generating CC and the sun is burning it off.

I’m kind of hearing that I haven’t killed something off by not bringing FC high enough in the recent weeks. Like it’s more than new stuff like pollen falling in, and more that once I get to 8-10ppm FC my SWG will be better at keeping up.

 

[YippeeSkippy]

Its not quite like too high of CYA makes the FC "less effective".... it just is all bound up and not much left to fight the good fight. Hence you need so much more to be available and that's not always practical.

 

[YippeeSkippy]

You have a heater on, right?? I only ask that because I otherwise would be surprised someone in your climate's water is warm enough for the SWG to be working already? Call me naive but you yankees have colder weather with your pools than I'm used to.

Maddie

 

[Kjp300]

I have a vinyl pool about the same size with an auto cover and a T-15 SWG. I keep my CYA at 60. When your cover is closed your FC should drift up like it did last year. In my opinion you are keeping your FC too low and it had dipped below the minimum FC level and you have the start of an algae bloom. Most times when you cannot keep FC levels up it is algae. With an auto cover not much debris or pollen should be getting in the pool.

I never let my FC drop below 5 and keep it in the 8 range. I always think it is better to be safe than sorry.

 

[jokerfive]

I have had my heater on, at least to some extent. We have a hot tub basically in the pool, so that’s been running a bit. But it’s been hot and sunny recently... pool went from 70-80f just naturally.
I added bleach to bring FC up. Recirculated and just tested. FC is 8.0 and interestingly CC is 0.5. Think we’re onto something. Will test in the morning again.

 

[jokerfive]

Ok, new results. This morning, opened the cover and did another FC test:
FC: 6.5 (down from 8.0 test previous night)
CC: 0.5

So I clearly have something in there, and was barely getting my FC high enough previously to do anything. Now that I'm getting in the right range, it seems I'm making some progress.

I just raised FC up to 12 and will continue testing.

 

[OHcabanaboy]

Are you running your pump all night? If not, you should be.

 

[jokerfive]

I'm not.... it's scheduled to run at 75% for 12 hours (7a til 7p). Would it be better to run it 24 hours on low (50%)?

The only reason I could see doing that would be having the SWG run longer, as I think my turnover would be sufficient either way.

 

[setsailsoon]

Joke,

With OCLT of .5 and no cloudiness looks like you could just have pollen demand on the FC. Almost any organic compound can consume FC. At 75% for 12 hr you are adding 2.7 ppm FC and still losing another 2 ppm or so which is definitely on the high end of the scale even for this time of year. If it were me I'd run the pump on low but sufficient speed to keep the flow switch on and adjust % power to stabilize the FC. Turnover is not a measure that we care about. Total flow through your pool should be determined by what is required to keep the pool bottom and surface clean. Most pools can accomplish this with very low flow and turnover. Surface usually requires high flow for only a couple hours to skim then low remainder of the run time. Bottom is cleaned by your cleaner so doesn't need any run time. You can use Pool Math to predict FC production for various combinations of % power and run time. I've found it is very accurate. Just select "effects of adding" from the menu top left. You should be able to produce 5.7 ppm with 75% and 24 hr. When I had to do this for pollen I'd just add a little liquid chlorine and my pollen blasts were short duration so it wasn't worth it to mess up my swg settings but this should work. After the pollen subsides you should be back to normal FC settings. If not, I'd look closely for any signs of algae since that's the most likely problem. If you find any, SLAM. If you're not sure SLAM, it can't hurt. Once you get these things done you should be back to easy pool care like last year. Lastly, cc test is very reliable. Mine would cycle from 0 to .5 all year round. Unless I had a cloudy pool, green, or visible algae .5 cc was very acceptable and my pool was always crystal clear.

I hope this helps.

Chris

 

[OHcabanaboy]

I'm not.... it's scheduled to run at 75% for 12 hours (7a til 7p). Would it be better to run it 24 hours on low (50%)?

The only reason I could see doing that would be having the SWG run longer, as I think my turnover would be sufficient either way.

I was just thinking that circulation while you're at elevated chlorine levels would be helpful in clearing up whatever is consuming your chlorine. At 1.5 overnight loss you're marginal on being okay. I think 1 or less is recommended. If above 1 you're supposed to perform a "Slam".

I didn't look to see what your slam level is but assumed since you brought it up to 12 there had to be a reason to do so and figured that was about your "slam" level.

Perform the Overnight FC Loss Test (OCLT)

The Overnight Chlorine Loss Test tells if the SLAM is finished or if you need to start a SLAM. This article says how to do the OCLT.

www.troublefreepool.com

 

[DHarv]

Something to consider that I overlooked as I was dealing with high chlorine demand on my new pool. I recently had landscaping installed around my pool and the landscapers ended up dropping a bit of nutrient rich soil into the pool. I didn't clean it up right away and my FC must have been at 0-1ppm for several days until it was all removed. Although my pool was extremely clear I could not get my FC above 1ppm without 100% output for 24 hours a day and I also realized my CYA had dropped from 60 to <20 (about a month between tests). I have a pipe run specifically for a pressure side cleaner, I usually have the valve closed off because I use a robot cleaner. My theory is that this dead leg of pipe could have been harboring nasties that weren't getting sanitized.

 

[jokerfive]

Thanks for all the insight and recommendations. I'm now at a 24 hour/day pump run time, with the SWG set at 40%. Will monitor how this goes.

Thinking more about it, I actually think I'm going to be chasing FC pretty regularly, even just given my pool design. Because I have the in-pool spa and it uses the same equipment... sometimes we could have the spa running by itself for 3-4 hours or more, which means nothing is happening to the pool from an equipment standpoint. After this type of usage, I find I need to adjust (up) my SWG to reach stability again and then lower it back down. Probably just means bigger swings for me in FC levels than a pool that doesn't have shared equipment (or a spa) like I do.

Will keep an eye on it and keep testing.