Little bit of algae with plenty of FC

[scott_f]

I have viewed this forum at times (mostly when I started up my new pool 4 years ago. In searching, I haven't really found an answer to my problem, so thought I would post it. When I took my cover off yesterday to go swimming, there was a little bit of algae on some surfaces, but the water was clear. this is the first time I have had algae in this pool.

I have a 12,000 gallon saltwater pool.

First, to start off 4 or 5 weeks ago (don't remember the exact date), I prepped the pool for the season. I keep a pool cover on through the winter (keeps Fc protected nicely), and when I took it off, didn't see any issues other than some leaves and bugs like normal. I brushed the pool, vacuumed out the junk, cleaned the filters and got all the chemicals balanced. CYA showed maybe 10PPM, so I added 4 lbs. and showed about 50PPM. Chlorine was I think around 2PPM, I added 1 gallon of liquid chlorine (so 10% solution) and FC was somewhere above 11PPM. Same thing I have done every year, and things seemed fine. The one thing I was not doing though was watching the phosphates.

Between then and now, I checked FC every week. It slowly went down, and when it reached about 5PPM, I turned on my SWG to keep it about that level. So, I am pretty sure my FC was never below 4-5PPM. I did not brush the pool during this time, and it was covered with a solar cover the entire time.

I take off my cover yesterday, and there is no smell, like there would be a bunch of CC, and like I said, the water was clear, but I had some algae growth. Where I way it was on some (not all) of the tiles used to show the steps, on the rim of the light in the deep end (that has a water jet above it), and on the automatic pool vacuum hose. None of these were covered in green, just some green. I quickly tested the FC again, and was showing 4.5PPM (I test at water intake to try and get minimum in pool). With that level of FC, I figured things are safe (better than lake water for sure) and we went swimming for an hour. the algae just brushed off easy.

After this I took a water sample to the local pool store to make sure my chemicals were good (I just got a new Taylor 2006 kit, so I assumed they were fine). What they showed was:
PH 7.6
FC 3.0 (I figured fine after swimming an hour in bright sun)
CYA 30 (I think this is a little low based on what I put in, so I figure we are somewhere in the 30-50 range)
Phosphates >1000 (as I said, I forgot about this one).

I brushed the pool again, cleaned the filter, and run the pump all night with SWG on, and my FC is back at 10+ (I had pool store measure since I had to get some phosphate remover, I was low).

So, how did I get algae growth? With a FC of 5+, and a CYA of 50-, I figured I would be ok. Is it possible that since I added the choline after the CYA at season start, that I just did not added enough to SLAM for the CYA I was measuring and that some algae was able to survive enough to grow on surfaces with the high phosphate levels?

Everything I have read makes me believe my pool chemicals were fine for preventing algae, but it appears I was wrong. Any help in understanding where I went wrong so I can not do this again would be great. Also, with the Fc back up to 10+ ( I will measure myself when I get home so see how high), should the algae be dead since I brushed it, or should I kick it up more to make sure I SLAMed it.

Any help would be great. For 4 years I have not had any issues, and this is minor compared to most algae issues, but it is bothering me what I am missing that allowed the algae to grow.

Thanks

 

[jblizzle]

Welcome to TFP!!!

Well, the biggest problem here is that you are trusting the pool store testing, which is wholly unreliable. You need to invest in one of the Recommended Test Kits. {EDIT: Just saw that you have the K-2006 ... so trust that and forget the pool store}

The only way to get algae is if the FC is not high enough as a function of your CYA level. See the FC/CYA Chart. Once you have algae, you need to follow the ShockLevelAndMAINTAIN Process to eradicate it.

Also forget about the phosphates ... you are just lining the pools store's pockets.

Please add your pool details to your signature as described HERE as it will help us help you.

 

[tim5055]

You got algae because you don't have sufficient chlorine. IF your CYA is 50 your FC should never be below 4. They tested it at 3.

A SLAM is a continuous process, not a one time addition of chlorine. Additionally, you need to use liquid chlorine; 8.25% bleach or 10/12.5% chlorinating liquid.
You need to follow the SLAM Process completely to the end.

How much Pool School have you read? Start with these:
ABCs of Water Chemistry
Recommended Pool Chemicals
How to Chlorinate Your Pool

Your purchase of phosphate remover tell me you are trying to mix pool store advice and TFPC advice. It won't work! Pick one and stick with it.

 

[scott_f]

Thanks for the replies. Just to comment:
jblizzle:
I did look at the CYA/FC chart (and I also knew from past reading to keep a minimum of 7.5% FC to CYA). Now, I know I did not shock the pool the first time, but this is because 1) the CYA was at 10 during winter and FC was 2-10 depending on when I put in chorine and 2) I saw no visible signs of algae the first time. Although my CYA is low for SWG, I do this before we start swimming because I have a cover on the pool the entire time and I want the liquid chlorine I add to have a better effectiveness. So, Until the pool SWG is turned on, I figure using the non-SWG pool should be good (requires higher FC for the CYA), so at 50PPM CYA, keeping the FC between 5 and 10 was meeting the requirement. So, I thought I was fine, since this has worked for 3 seasons already.

tim5055: I believe the FC was 3 when they tested it because 4 people had been swimming in the pool for an hour. Before we got in, I tested the water at the intake (skimmer() and it was 4.5. I have read a decent amount of this forum 4 years ago when I had the pool built, and for 4 years, no problems, so, no, I haven't been here recently. My purchase of phosphate remover was grasping at straws to explain something that did not make sense to me (no visible signs of algae a month ago, and having a 5+ FC the entire time, well until maybe a few days ago, not sure when it got to 4.5).

So, yes, I did not shock the pool a the start, just had a high level of FC, and maybe there was some algae that was not visible at that time that survived. But this was because I had no smell and no visible signs of issue with the water. So, do you believe that is what it was? That there was algae in the pool that was just not visible, and even though I had a high level of FC, it was not shock level so the algae was able to get some foothold on some surfaces? I guess at some point in the winter algae got a foothold and it wasn't until the warm weather (pool is 86F degrees now) that the growth became visible. since I have a cover on all the time, I did not see it happening (trusted high level of FC was protecting me).


I will test my CYA and FC myself again and follow SLAM to ensure it is all dead. So, even though I see no signs of issue, and have kept a good FC through winter, I guess I should make sure the high FC meets the CYA chart for shock at start of season.

Thanks

 

[scott_f]

Oh, just one other thing. When I did raise the chlorine the first time, with the SWG off, and a solar cover on, the FC dropped about 1PPM to 1.25PPM per week (which I think is fairly slow when not having any source of chlorine being added). So, I also used this as a assumption of there not being any issue for that month. Everything I have read about algae and dealing with it says it eats up chlorine fast. So, is this not a good assumption to use?

If you can't tell, I am frustrated because everything I knew of as a sign to look for told me there should be no issues. Slow FC loss, no chlorine smell you get with high CC, clear water (algae was just on a few surfaces that were not near my skimmer, so I did not see them until the cover was removed), high level of FC for a month (just not shock level).
Thanks

 

[tim5055]

Scott,

The only real "sign" to use is your test kit. Keep the FC above the minimum all the time and you should be good to go. While cold water slows algae growth, it doesn't stop it. Many people stop testing and adding chlorine during the winter because they are not using the pool. Even in the winter you need to test and adjust your pool unless you close it.

As Richard is away today I will borrow his line: "A pool is like a pet - you have to feed it every day, even the days you don't want to play with it!"

 

[jblizzle]

Your frustration is understood.
How much were you running the pump over the last month? The pool was not just sitting "stagnant" was it?
Maybe the algae formed in areas with low water flow and thus locally the FC level dropped.

 

[scott_f]

tim5055, I try to keep an eye on it during winter. I will go and add a bunch of chlorine so I know it is good for a while (pool is covered all winter to cut down on things getting in the pool and sunlight degrading the FC) and check it and when I see it get low, I add more, but I will be honest and say I don't check it every week or other week in winter, so although I believe I kept it high enough all winter, there might have been a time when it got to the 2PPM, and the CYA was still above 20. I will make sure to be better next winter on this part I really do take care of my pool. This is the first time in 4 years that there is any sign of trouble and I got compliments from people about how clean and clear my pool always looks (thanks in a good amount to this forum 4 years ago when I studied up on having a new pool and keeping it going).

jblizzle, I run the pump 8 hours a day (9AM-5PM to cover the time the pool is in the sun) at a flow of around 2500-3000GPH (I have to look again what RPM I have the pump set at), so somewhere between 1.5 and 2 times turn over each day. So, I should be having pretty good flow. I was thinking the same thing about low flow areas, but what got me was the vacuum line was one of the things that had visible algae, and it moves through the water a couple times a week (so, again, confusion that low flow doesn't seem to answer it).

Again, thanks for the help and ideas. To be safe, I am going to add another gallon of chlorine in when I get home to make sure I am above shock level and will keep it there. A question on this, I know SLAM says to keep it there for a few days adding liquid chlorine. Is there a reason not to have your SWG going and keeping it up once you use liquid chlorine to get it up? Does that high level of chlorine have a negative impact on the SWG (when running)? I didn't think it did, since you can use the SWG to super chlorinate, and it would make it a lot easier to maintain a constant high level of chlorine.

I guess another question, with having only a small amount of visible algae, and FC was holding steady with my normal SWG setting (at 10% when no one is swimming) and that running overnight with SWG at 20% raised FC to 10+, do you think algae is still present? The thing I am struggling with is that you want a high enough FC to kill any algae that flies/floats into your pool from the air, so the minimum FC is supposed to meet that, right? So, I am thinking that when I brushed the pool, and broke up the algae off the walls, and that little bit of algae has been exposed to well above minimum FC level, it should be dying right? The high level of FC when shocking is to deal with the CC you get from killing a lot of algae in a green pool, correct (so you need to keep it up there since you have a lot of algae to kill). But, if I am not showing CC (I will check again when I get home)and have a well above minimum level of FC, shouldn't that be killing the algae, since no CC and minimum level of FC (minimum meaning what the CYA/FC chart shows) is all that is needed to kill algae that flies into your pool? Am I making sense about what I am asking and my logic here? With no CC and a good amount of FC, algae should be dying, shouldn't it (of course this gets back to my original confusion that I thought I was fine about not getting algae in the first place with my FC and CYA levels).

The one thing that comes to mind is that, maybe when I measured CYA, I did it too soon after adding it (I think it was 24 hours of pump running) and it is actually higher than 50 (I don't trust pool store either, but I will use them as a check against my measurements if something seems off), and when my FC did drop below 5 (to the 4.5 level) it was enough to allow algae to get hold (even though CYA/Fc chart says SWG pool of 70CYA should be fine with 3PPM minimum and 5PPM target).

Thanks.

 

[jblizzle]

Just follow the SLAM process until you pass the 3 criteria to stop ... if there is nothing left to kill, then it will end very quickly.

You need to wait a week after adding CYA to be sure it shows up on the test.

Sounds like you are actually running your pump for longer and at a higher speed than should be necessary. See: Determine Pump Run Time.

 

[tim5055]

Scott,

As Jason alluded to there may be a hidden nook/cranny in your pool that is harboring a little village of algae. Some people find it behind the pool light, others find it under a stair.

It can be frustrating. But follow the system and everything will be killed.

 

[scott_f]

Ok, thanks. So, just a coupe things.

1) my question on using the SWG to keep the FC at shock level, is this ok to do? I would think it would do a good job of ensuring a constant FC level.

2) Except for the level of FC to shock level, my pool already passes the criteria of SLAM ending (and has actually passed the criteria for the whole month). <.5CC, holds FC (last week I was at 5.5, this week 4.5, so only 1PPM in a week), and water is clear (always has been, just a few surfaces with algae, no cloudy water). So, it sounds like I just get the pool to shock level (well 1PPM higher to handle the 1PPM loss test) and I am done, since I expect the FC will hold as it has been doing for the past month.

Oh, and yes, I do run my pump more than needed, as I don't mind a little extra power cost for ensuring plenty of water flow through my pool since I try to ensure my pool is safe for swimming (which seems ironical that I got algae when I tend to be conservative on pool care especially during swimming season).

Thanks again, I will shock my pool, and then take the cover off in 24 hours (I expect it to be <1PPM loss in 24 hours) to get the FC down so we can swim again (other wise it would be another few weeks before I lose that much chlorine).

 

[jblizzle]

1) It might help maintain the shock level, but will put wear and tear on your cell.

2) If you see algae, that fails the clear water portion. And make sure you have the SWG off when you do the OCLT.

It is perfectly safe to swim at FC levels up to shock level.

 

[scott_f]

Hehe, ok, I guess one more thing. In reading SLAM again, it doesn't say the end criteria has to be met at a high FC level, just that you need <.5CC, clear water, and not lose more than 1PPM FC overnight. So, since my water has always been clear (I can see the pebble sheen rocks a the bottom of the deep end, and don't notice any greenish color), my CC < .5, and I brushed my pool last night, if I hold at the 10 (or whatever it is at above 10 right now) PPM FC overnight, does that qualify as passing SLAM? Or is it implied that you have to hold shock level FC overnight?

Thanks

- - - Updated - - -

Ok, so I thought clear water meant not greenish tint. So, I will turn off SWG tonight, let the pump run, and check FC tomorrow. If there is no loss (and there is no green surface anymore since I brushed last night), I am good.

Thanks.

 

[jblizzle]

The criteria were written assuming that you are starting at shock level.
That said, for doing the OCLT in this case, you may not need the FC to be all the way at shock level. I just do not like to do the OCLT at normal maintenance levels as a 1ppm drop seem more significant to me when it is 25% of the chlorine as opposed to 5% or whatever.

 

[scott_f]

Ok, thanks. I think I will do the OCLT at the current level (at least 10PPM) as that will be reasonable for the 30-50PPM CYA level, and if I don't see a drop (might even say a .5PPM drop in this case, to cover the lower than shock level) I will consider the pool clean ( I really do believe it is clean, with how little algae there was, but having a criteria let's me know a good rule to go by).

Thanks

 

[ivyleager]

no chlorine smell you get with high CC, clear water (algae was just on a few surfaces that were not near my skimmer, so I did not see them until the cover was removed), high level of FC for a month (just not shock level).
Thanks

I rarely get an ammonia smell with my algae blooms. Even clearing my pool last week when I opened it, I had no smell and my pool was a SWAMP.

I've had "little" blooms like you describe. It took me awhile but I finally attributed it to circulation. My pool (see signature) has only 1 skimmer and 2 returns. If my pump is not on for 12+/day, I get the algae you describe, regardless of my CL number. Which is why I generally set my minimum higher than what is recommended for my CYA level. During the hot summer days when the pool gets a lot of activity, I leave my pump on 24/7.

Moreover, I lost ALL my CYA over the winter. Closed with a CYA level of 40-50.

Hope this helps.