FC is right but I can still see some algae forming

[slepax]

Hi all,

I had an issue with algae about two months ago. Getting the Taylor kit and following recommendations on this thread I have set my SWG to 50% capacity. The last two tests have shown that FC is around 4-4.5 ppm, with CYA levels around 70-80 ppm, and CC has always been quite low (0.5 ppm or less)

I checked the pool this morning and I could see small patches of algae forming. The pool is not sparkling clean as we have had some high winds over the last couple of days and sand has blown in, but it is clean enough. Furthermore, the pool has not been used for at least 4 days now (we've been travelling).

I have only noticed it this morning. I decided not to do anything about it just yet because I first want to confirm this is really algae (sometime it's easy to confuse with sand), but it does look like it as sand can not stick to the side of the walls

Being that my chemistry seems to be right, what could be the cause of the algae forming?

Thanks!


PS - it's been a while since I last backwashed (I'd say 6 weeks or so), nevertheless the pressure on the sand filter is still relatively low. Could it be that algae is forming inside the sand filter which effects the rest of the pool, and that's even though FC level is right?

 

[pwrstrk]

When you had algae previously did you SLAM the pool ? Do you think while you were away your FC level slipped below the min level for some reason ?

 

[zea3]

When you had your earlier algae bloom did you follow all the steps to complete the slam process ? It is possible for there to still be some live algae in the pool if you did not complete the slam process. Also sometimes algae can pop up in areas of poor circulation. Brushing the pool helps insure the water is mixed well and distributes chlorine more evenly.

 

[slepax]

When you had algae previously did you SLAM the pool ? Do you think while you were away your FC level slipped below the min level for some reason ?

I did SLAM the pool and although it's impossible to know whether I still had algae left the water turned completely grey and was very unclear.
I hardly believe FC ever fell below that level. FC was quite high when my SWG was running at full capacity, and the new FC level matches the calculations of my SWG production rate and filter run time.

When you had your earlier algae bloom did you follow all the steps to complete the slam process ? It is possible for there to still be some live algae in the pool if you did not complete the slam process. Also sometimes algae can pop up in areas of poor circulation. Brushing the pool helps insure the water is mixed well and distributes chlorine more evenly.

It was hard following the SLAM process properly as I didn't have the Taylor test kit at the time. I would say that if anything I've over killed it in terms of adding chlorine to the pool. It wasn't just a matter of one hit I did repeat the process a few times.

Poor circulation is an interesting point. I have a variable speed pump and I have been running it on low for the last month or so. Although in theory it should cycle the pool water twice in those 8 hours, it may not reach every point of the pool as you mentioned. I used to scrub the pool walls once a week but we've been travelling so I didn't get to do it last week.

I have scrubbed the walls lightly this morning, but not fully. I know some [suspected] algae is still there. Would it be ok to do a scrub and bump SWG to max for a day? (this should result in ~9-10 ppm FC), Or do I need to SLAM?

 

[zea3]

I would go ahead and do the slam process. It should go fairly quickly and then you can see if the algae comes back to the same area.

 

[pwrstrk]

I agree. With visible algae SLAM the pool. Make sure you follow the instructions to the T !! Remember the three criteria you need to meet to stop the SLAM process. Turn your SWG off for SLAMMing.

It sounds as if you might not have did the first SLAM properly.

 

[Patrick_B]

I agree, if there is still Algae, you need to kill it with a full SLAM.

 

[slepax]

Thanks all, but I've decided to wait. I came home after work and was very indecisive on whether this is algae or not. Just too hard to tell because of the angle of the sun and amount of sand around. I asked my wife and she couldn't tell either.

The water is still sparkly clean, with hardly any cloudiness. I don't want to SLAM for no reason. So I've vacuumed the pool and now it's clean, I will take a reading of FC now and also before sunrise, it should still indicate whether there is something in the water. This will also give me the opportunity to inspect the pool in the morning without any sand.

I know it's better to hit algae early on but I don't want to hit something that's not there. I'm still learning so for me it's far more important to understand whether my current settings are adequate to prevent algae, and for that I need to know if I do have algae. I bought the liquid chlorine just in case, so if I see algae in the morning I can start the SLAM immediately.

 

[Leebo]

Try an OCLT tonight. By eliminating the sun you'll see if there is anything growing in the water.

 

[slepax]

Thanks for the link, that is exactly what I am aiming to do. The only thing is that instead of shutting off my SWG I have allowed it to run as usual and will take the reading 30 minutes from when it's done for the night. This should still allow for more than 7 hours of no chlorine being generated so hopefully this should be enough to see what's going on. I think this is a great routine.

I was also thinking of backwashing so I know everything is clean and even the filter is "empty", but then I will have too much water lost and might mess up my CYA levels if I needed to SLAM so decided to leave everything as it is.

 

[slepax]

So the night test showed a drop of 1.5 ppm in FC over a ~7 hours span. I had 4.5 ppm last night and then 3 ppm this morning. This is somewhat borderline especially considering I found a few bugs and a live bee taking a swimming, not sure how long it's been there and how much is insect consumption on FC now days.

Interesting part is CC was 0. My understanding is that CC increases because of chlorine being consumed, so would you not expect CC to go up? Still learning so maybe I'm missing something here.

The water still looked clear, but not as clear as I had it in the last few weeks and so I've decided to start the SLAM anyway. I've dropped 6 liters of liquid chlorine 12.5% (125g/l, I assume that's 12.5%?) around the pool area. The problem is that I'm not home during the day so can't really monitor/adjust. Hopping for the best ...

Couple of questions:

- I have set the pump to run 24x7 but that's on low, is that enough? I can supplement one/twice a day with scrubbing the pool.
- I have turned the SWG off as per the guide, but do I really need to do that during the day? I understand the reason of doing it during the night.
- Not too long after I dumped the liquid chlorine my acid dozser alarm went off saying ph is now 8.7, does that make sense? Update: the SLAM guide actually mention that ph will go off the chart, so I guess I should turn my acid dozer off?

Thanks!

 

[jblizzle]

That is not borderline. Only 7 hours and starting with FC of only 4.5, you probably should not have dropped more than 0.5ppm. You definitely need to follow the entire SLAM process correctly.

You can leave the SWG on if you want to help maintain the FC level. We recommend having it off so you get a sense of the FC consumption.

Leaving the pump on low should be fine.

Did you lower the pH before starting the SLAM? Can't measure the pH when FC is greater than 10ppm. Probably should turn off the acid.

 

[slepax]

Did you lower the pH before starting the SLAM?

Yes, it was around 7.4 to begin with.

Can't measure the pH when FC is greater than 10ppm

So does that mean liquid chlorine is absorbed really (really) fast? It didn't take more than 5-7 minutes for the ph to shoot up.

 

[jblizzle]

It is not absorbed. The test reagents do not work correctly when th FC is too high. The pH test will read higher than reality. Although the pH is somewhat higher due to adding the bleach to get to a high FC level as well, just not as high as the test shows.

 

[slepax]

Just a quick update, to make sure it makes sense.

I only needed to add liquid chlorine twice, 6L in the morning and another 3L in the afternoon. I checked my FC at night and it was 21 ppm, checked again this morning and got exactly the same result (no bees swimming this time, and the pool was very clean).

Water was clear even before but it's back to looking very crisp again.

CC was 0.5 ppm or less.

SWG is still off, but I've left the pump running still on low speed.

So I assume I'm just going to leave it at that?

Thanks!

 

[jblizzle]

Sounds like you have passed the 3 criteria to stop the SLAM. Just let the FC drift back down and fire the SWG back up to maintain the appropriate FC level ... I would try to keep it right around 6ppm.