Algae or just simply dirty??

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PatG25

Hi everyone

I have owned my pool for about 3 years now without any major problems. Had some questions in the past that the great folks here at the forums helped me out with.

So now I have what seems to be a basic question. No problems with my pool all summer long. Last week I went away for a few days and came back today. Well, the pool was green. All the chemical readings are in the correct range, with Chlorine coming in at 4.5 (it's a salt water pool). So tonight I got out the brush and started brushing the pool. The "green stuff" simply moved, just like dirt. Put in my pool robot and could see right away the bottom of the pool where the pool robot went over.

So is it dirt or is it algea? I had algea on certain spots on my pool before and cleaned it, so I guess that it would be dirt. However, the pool is "green"! So can you move algea around with a brush? How can algea form with chlorine and stabilizer in the right range? One thought I had was that my pool cartridge filters need cleaning, but I do clean those every month (also PSI has not increased, so they should be OK).

So tomorrow I will vacuum the pool. But if it is dirt, how can a pool get this dirty in 5 days? Or is it actually algea??

Thanks.
 
PatG25 said:
How can algea form with chlorine and stabilizer in the right range?
Thanks.
Click to expand...

Because they have to be at proper levels in relation to each other. Very often they are not, and we find this to be the case here on a daily basis. You do need a SLAM without question. However, as mentioned above, we are all about the numbers around here.
 
OK, so here are my readings:

Free Chlorine - 2.5
Combined Chlorine - 0
CYA - 60-70
Ph - 8.2
Alkalinity - 110
Calcium Hardness - 220
Salt - 2630 ppm

It is a Salt Water Pool. The pH is high as we have been out of town for 6 days, but I do normally watch it carefully being a Gunite pool. I have seen some algea here and there over the past week that I have brushed away. I also brush the pool every week. I will take another Chlorine reading in the morning to see if I lost any Chlorine. Right now everything is shut down and no chlorine is being fed into the pool.

So to me it looks like I have to shock the pool, even though I still don't quite understand how it turned green so quickly. Before we left 5 days ago I could see a "twinge" of green in the pool, and I threw in a couple of Chlorine tablets into the feeder just in case. The salt is low so I need to add that, too.

I reviewed the SLAM method; my wife today went out and bought 6 bottles of 12.5% liquid chlorine. I guess my free chlorine is low but I could never figure out how to get that to the 5 ppm range just with the salt generator unless I run it at 80% all the time. And the darn thing is new!

Looking at the pool calculator looks like I have to throw in 4 of the bottles of chlorine.

Thanks!
 
Right off the bat I can tell you that Chlorine at 2.5 is too low for that CYA. It doesn't matter that you get your CL from a salt water chlorine generator or from a bottle, it's just too low.
Your pH is also too high.
How long a run time do you run your pump/filter/swg daily? Running it longer yet on a lower percentage might help you. I always use liquid bleach to supplement my SWG when I want a boost.
 
Yup. FC is too low and your pH is way too high.

And your FC is much to low to do a good OCLT.

You need to SLAM and it is going to take WAY more than 6 bottles for your pool size. You need to maintain the FC at 28ppm until you pass the 3 criteria to stop (with the SWG off). In fact, it is going to take you 8 of the 121oz 8.25% jugs of bleach just to get up to shock level initially. And then you need to be testing and adding more bleach every hour or so at the start.

Do you have the FAS-DPD chlorine test to do this correctly?

BTW, what size SWG do you have? Is it way undersized where you think you have to run at 80% all the time?
 
Thanks for the quick replies!!

Yes, I realize the my ph is high. As I said, it crept up on me in the last week as I have been away. Should have checked it before I left. The chlorine numbers were obtained using the FAS-DPD test, so I do trust them. I run the SWG from about 10 am to 6 pm daily, at 40-60%. Turned it down since it got cool. When it was hot I was running it at 80% but could not get the free chlorine above 2 ppm. So I supplemented with chlorine tabs, but wasn't really diligent about that. I did add more stabilizer a few weeks ago to bring by CYA up; I thought that was the reason the SWG didn't quite work right. It was only around 45 at that time. So maybe the CYA increase with the 2-3 ppm chlorine (not enough) caused the algea to form?

I have 6 bottles of 12% chlorine (not 8.25%), per Pool Calculator 4 bottles should get me up to 26 ppm. I'll get more if I need it.

OK, but then what. How long would I need to keep it there given that my current CC is 0 already. Or do I just look at the OLCT? How much FC do you need to do a good OLCT? Should I just slam it, then measure OLCT from that point on? However, I am at work all day so I can only do this in the morning and the evening.

One other question - I did read it here that it is safe to swim up to the shock level. It seems high to use the pool with that much chlorine in it.
 

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The CC are 0 now, but they may go up when you start. Not sure how to be more clear than the SLAM article. You do it until you pass all 3:
1. CC not > 0.5ppm
2. Water is clear and you see no algae
3. You pass the OCLT

You need to test and does back up above shock level as often as you can. The better you maintain the FC, the faster the process goes.

Yes it is safe to swim up to shock level ... but to SLAM you should be above that. Once you pass everything, you can swim as soon as the FC drops below shock level.
 
One last question. My pool is going to be open another 3 weeks or so before I have it closed. Is it worth trying to get rid of the Algea now or should I just let it go until next season. Is it dangerous to swim in the pool with Algea present? School has started, so the pool isn't going to be used much.
 
It is not dangerous to swim with algae if you maintain a decent FC level > minimum, maybe a little higher than normal.

ASSUMING!!!! you can see the bottom of the pool. If you can not see the bottom, NO SWIMMING!!! It is just not safe due to possible drowning.
 
If it is clear enough to see swimmers in the deepest part and if you maintain your minimum FC per the chlorine/cya chart, it should be safe for swimming. Algae will not hurt anyone, but having chlorine in the pool is important to reduce person to person transmission of disease.

Still, I would do the SLAM process and if you want, let your FC drop below the SLAM level for your cya level when you want to swim. That way you close to a clean pool and hopefully you can open to a clean pool as well.

I would not close the pool until the water temperature is consistently below 60F, so you really don't know when that is until it gets here.
 
I would not consider an FC of 2.5 to be that bad on a SWG pool. The target range with CYA of 70 is 3-10. I have dropped a little lower than that without any issues in the past.

My recommendation would be to run the OCLT to make sure you need to go through the SLAM process. If it were me and I knew there was only 3 weeks of swim season left, I would leave it be and simply supplement with bleach until closing. You can address any issues when you open next year.
 
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