FC levels continuously low

dpool2

Member
May 28, 2017
11
holland,mi
Good Day.

First full year with a 10 year old AGP. All going well this summer here in Michigan. We installed a heater this year, replaced (and increased from 16" to 24" sand filter). There has been no real issue with algae. I have been having a hard time ever getting any FC when I test (K-2005). The pump/heater turns on about 10am and turns off around 8pm. Typically I think can see underwater across the pool with no problem (17') (never really thought to keep a mental note of actual viewing distance -- will do now).

I routinely vacuum the pool on Fridays, and test at that time and on Wednesdays (using the TFP Pool Math app to tell me what chemicals to add). All summer long I have never had a reading of FC (always zero).

Last Wednesday, started 3 days of good rain and I didn't get to vacuuming nor testing the water.

Saturday came and there was green-ish algae starting to grow on the bottom. So, I vacuumed well, brushed the walls, and added 2 gallons of chlorine per Pool Math and one pouch of Clorox Slam Step 3 pouch -- chlorine and algaecide). I've left the pump on 24/7 since Saturday (but turning the heater off over night). We are still swimming, and all "feels" and smells okay, but the water is definitely the cloudiest (more of a white rather than green cloudy) that I've seen it this summer.

Sunday I tested again, vacuumed again, and backflushed and rinsed the filter (it didn't look too bad). I also added about an inch of fresh water Sunday night as the level was getting toward the bottom of the range on the skimmer (city, hard water). While swimming later in the afternoon, I could definitely smell the chlorine.

Today, Monday, the water looks better than yesterday (less cloudy) and the Pool Math told me to add another gallon (121 oz 8.25%) of bleach. Tonight while swimming there was some algae on the floor, not a lot. Still white-ish cloudy. Today I actually had a FC level. Didn't notice any chlorine smell.

Any thoughts or comments appreciated. Attached photo is tonight at sunset. I would have taken a picture of the algae, but we've been swimming and I made sure to go all around and "wave" the algae away so that it would be suspended.

Thanks.

PS. Pool Math app -- as I go back and look at my logs, it doesn't appear that I can access what the recommended levels of chemicals it suggested.



FCCCpHTACHCYACSI
2017-07-10
(new filter installed)
007.812025020.22
2017-07-22007.811023015.17
2017-07-2900.57.69025032-.08
2017-08-030.50.57.48042-0.37
2017-08-11007.48026042-0.35
2017-08-1300.27.446-0.42
2017-08-20017.47023058-0.50
2017-08-211.57.28023052-0.64
 

Attachments

Jimrahbe

Mod Squad
TFP Expert
LifeTime Supporter
Jul 7, 2014
20,267
Bedford, TX
dp,

It appears to me you have a low level algae bloom. To confirm this you need to run the Overnight Chlorine Loss Test.. (OCLT)

Here is how... Overnight Chlorine Loss Test The hardest part is getting up before sun rise... :cool:

What FC level are you trying to maintain?

Are you adding more CYA or is something else making your CYA go up???

Thanks for posting and let us know the test results..

Jim R.
 

dpool2

Member
May 28, 2017
11
holland,mi
Ok, I'll run the OCLT.

Not sure what to keep the FC at. Pool Math says range should be between 4-8. I was just always surprised that it was at zero nearly every time I test.

Probably back in early July I added some CYA per instructions of the Pool Math app (which is why I wish I could find in the app where those past recommendations were/are). But it was only one time, and based on my logs, it looks like my CYA jumped between July 22 and July 29, so I must have added it then. I did notice the trend upward, but the upper range seems to be suggested at 50, and now that I'm sitting at 52....
 

Jimrahbe

Mod Squad
TFP Expert
LifeTime Supporter
Jul 7, 2014
20,267
Bedford, TX
dp,

With your CYA say 50... your FC should be about 7 with the absolute low of 4 ppm.. See this chart..[FC/CYA][/FC/CYA]

Thanks,

Jim R.
 

dpool2

Member
May 28, 2017
11
holland,mi
Wow. 7. I'm going to need a lot of chlorine.
Guess I shouldn't rely on "there's an app for that" to much.
So, I'll head out and start the OCLT test then to the store for some chlorine.

As fate would have it, the family is leaving for 8 day vacation on Saturday. There will be a house sitter that will want to swim.

Q: How fast should I try to raise the FC to 4-7? All in one day? Over the course of a couple days? Almost seems like it would equate a bit to a SLAM. So maybe starting a SLAM would solve two issues...1) kill off any algae, and 2) raise my FC ???
 

BasicTek

Bronze Supporter
Oct 9, 2016
875
Lake Mary, FL
You can use pool math to raise your FC all at once, How are you getting those CYA numbers with a Taylor 2005 kit (the vial should only have round numbers)? If you have algae you're going to need to SLAM and that's not a 1 time thing you have to maintain your FC constantly until the problem is gone. This will also require an FAS DPD chlorine test that doesn't come with the 2005 kit.
 

dpool2

Member
May 28, 2017
11
holland,mi
I do not have a FAS DPD test. And as for my CYA numbers, those are a guesstimate based on where the water level is between two marked values as the vial does only go in 10s (so, half way between 50 and 60 I notate as 55, etc).
 

dsmith99

Silver Supporter
Jun 18, 2016
238
SW, Iowa
The CYA test is 50 or 60, there is no marks between and you'll notice the numbers aren't spaced the same, the test is readable in 10's.

You should avoid the Clorox packets of anything and stick with liquid chlorine or bleach. Most dry chlorine products add CYA along with chlorine and can get you in high CYA trouble pretty quick. Any of the "blue" clorox products most likely add copper too, and you don't want that.

With the cloudiness of your water I probably wouldn't even bother with the OCLT just yet and get started slamming. With a CYA of 60 your SLAM level chlorine is 24 ppm, you might need more bleach than you thought.

Most of the K-2005 works fine, but you're gonna need to add the FAS/DPD chlorine test to SLAM. It can measure the high FC levels with .5 (or even .2) accuracy rather than just offering you a useless range like the K-2005 dpd kit tests. Slam level with your CYA is probably over what the k2005 dpd can even test.
 

dpool2

Member
May 28, 2017
11
holland,mi
Ok, I just consulted PoolMath here on the TFP site, and it says I need to add a bit over 1-1/2 gallons of 8.25% bleach (1.7 jugs). That is actually not very much. Which circles back to my topic title: "FC levels continuously low"

Prior to this algae problem this weekend, I've had good quality water (no algae, no slimy feel, no smells, no rashes, etc, could easily see pretty far underwater -- further than now). And my FC levels are always near or at zero. What the Pool Math app is suggesting that I add, seems to be correct (as the calc on site here says to go from 0 to 7 only takes 1.7 jugs and the app routinely suggests I add between 1 and 2 jugs of chlorine). I'd say most of the time I'm taking my test readings mid morning -- say 10am-ish.

It's been 20 years since I've taken in- and organic chemistry classes, but I'm pretty sure I understand the relationship between FC, CC and CYA and sunlight, and if the pool wasn't pretty well balanced, I'd have expected to have an algae issue much sooner than now.