Does a green pool definitely mean algae?

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amersonl

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Jun 1, 2008
38
North Carolina
The pool was a little murky and dirty from rain, pollen, etc. and we though vacuuming and filtering would help clear it up. Yesterday it looked a little green and today it looks very green. However, there are no CC whatsoever. The FC doesn't appear to be dropping quickly either. We do have a high pH. Is this an indicator of algae? I will test again later in the day to see if the FC changes, but here are the numbers as of 5:00 p.m. Oh and I am using a TF-100 test kit.

FC = 4.5
CC = 0
pH = 8.2
TA = 50
CYA = 30

I know the TA is a little low, but we have been keeping it at 70 all summer and have not had any problems. Thanks in advance for any help!
 
A high pH I don't believe is an indication of algae, but the high pH will interfere with the ability for the chlorine in your pool to be effective.

While there are other reasons a pool might turn green not related to algae (chemical reaction, dirt type in your area), the fact that yours is getting greener makes it extremely likely it is algae.
 
Since the FC isn't getting used up quickly, I'd try lowering the pH to see what happens. If lowering the pH clears up the water quickly, then I'd suspect copper and you can get your water tested for metals. You could then lower the pH more until the color goes away and add a metal sequestrant and/or do some water replacement.
 
amersonl said:
Ok, so we lowered the pH successfully yesterday and allowed the pool to adjust overnight. It is still a bright shade of green. Our FC dropped from 4 to 3 in 12 hours. Still no CCs, but we are going to shock and see what happens.
Click to expand...

What are you using to bring the pool up to shock level?
 
I am using bleach to shock the pool. The pool calculator said for my numbers to bring the FC up to 13. So I did. Here's what has happened so far.

11:30 - FC=12.5
12:00 - FC= 14
12:30 - FC=13.5
1:00 - FC=13.5
2:00 - FC=12 added bleach to bring up to 13
3:00 - FC=12.5 added bleach to bring up to 13

STill no CCs as usual
My husband brushed everything at 1:00.
The roboKleen vacuum is working the bottom and the pump and filter are set on high.
The pool still looks exactly the same - green. It has only been green for three days. How long before I should expect to see a difference? Do I keep the pool at shock level until I see a difference? Thanks for any help!
 
Based on your description and FC usage, that's not algae.

About the only two things that cause a green pool is algae or copper. Have you applied any copper products into the pool.....some ti\ype of alternative sanitizer? Not just a quart or so but something (like a froggie) that has been putting copper ion your pool for a long time?

Can you post a pic?
 
We have been using the BBB method since we put the pool up and filled it in June. It has seen nothing but bleach, baking soda, stabilizer and pH decreaser (yesterday). We have not added any water ourselves since sometime in July because we have had so much rain. We actually have drained water out three times in the past three weeks. We got 10 inches of rain overnight a few weeks ago and had a lot of rain again last week. The pool has been sparkly with an often dirty bottom since we opened it. I'm not sure how to post a picture. I have one, so I will work on that. Thanks!
 
Try lowering the PH down to about 7.2 and see if that has any effect on the color.

Your TA level is also quite low, and lowering the PH will lower the TA even more. You should add some baking soda to raise the TA after lowering the PH.

You should also do any overnight FC test. Check the FC level in the evening, at least half an hour after the last chemical additions of the day. Then test the FC level again the first thing the next morning. If the FC level remains the same overnight, or is within 0.5, then you don't have algae. If the FC falls by 1.5 or more overnight then you do have algae.

You you have any reason to suspect there might be copper in the water? Copper tends to come from copper based algaecides or from having the PH really low (below 6.8) and a copper based heat exchange coil in your pool heater.
 

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We are quite baffled needless to say. We have no idea how copper might have gotten into the pool if we don't have algae. We have only put bleach in the pool. We do not have a heater, nor has the pH ever fallen below 7.2. I put pH decreaser in yesterday when the pH was 8.2 and brought the pH down to 7.2 this morning. This afternoon the pH was back up to 8, but we thought this was because we had a high FC from shocking. When the pH read 8 I also tested the TA which was 60. I went ahead and added baking soda, but did not do anything for the pH this time. Should I add some pH decreaser again even though the reading might be off?
 
Thanks for the pics....that doesn't look like algae and your FC tests indicate it's not as well.

Could someone have dyed your pool? I'd still think chlorine would reduce and eventually eliminate that (dye) but it's the only thought I have.
 
Adding a lot of bleach can raise the PH temporarily. I suggest leaving the PH alone till the FC level is below 10, and then test the PH again and seeing where you are.

If it was copper, getting the PH down to 7.2 should have had an obvious effect.

Nearly all dyes would fade at least somewhat after 24 hours at shock level.

Doing the overnight FC test would be very interesting at this point.
 
well, I'm not convinced.

It doesn't look like any algae laden pool I have seen before

You were somehow able to hold FC during the day with very, very little loss. If that green was algae, I would expect at least a 50% drop in the available FC.

If no one dyed your pool, I remain stumped but I do not believe that is algae.
 
I'm not familiar with your type of chlorine feeder. Can you explain to me how it works? Was it somehow supplementing your FC level, which might explain why there was minimal loss if this is algae? Does it use liquid chlorine or tablets? I looked at your pics, boy is that bright green! Kinda looks like the Chicago River on St. Patrick's day..... :shock:

We normally credit a 2ppm overnight loss to organics. So I'm confused if Dave is confused too. Hopefully others will chime in and we can figure this one out.
 
Some algaecides contain copper. I would suggest that you have a copper test done at the pool store. If there is no copper, I'm thinking that you may have mustard algae mixed with green algae, which would give you a yellow green color. Mustard algae is very resistant to chlorine. You could try adding two pounds of "Yellow-Out" to help clear the mustard. Your pH should be over 7.5 when using the "Yellow-Out". If your pH is below 7.5 add 6 pounds of baking soda and wait 8 hours. Then add the two pounds of Yellow-Out, wait 5 minutes then add 2 gallons of bleach. After 24 to 48 hours add another 2 gallons of bleach.
 
Yellow/mustard algae is usually like dust and grows on the bottom and sides, usually where it's shady. It shouldn't color the water unless it got stirred up. Yellow Out is most useful in pools with very high CYA since in that situation it would take very high FC levels, but this pool only has 30 ppm CYA so chlorine alone would be able to kill yellow/mustard algae at around 18 ppm FC. I don't think there is yellow/mustard algae in this pool.
 
All of the heavy rain associated with the occurrence of the algae and the look of the pool and the color all lead me to believe that this is a mixture of mustard and green algae. The automatic roboKleen vacuum is keeping the mustard stirred up. I have had good results with "Yellow-Out".

The pool has not reached an 18 ppm chlorine level yet. I would suggest the copper test. If there is no copper, I would recommend that the O.P either raise the chlorine to 18 ppm or use the Yellow-Out. I don't think that this is any type of dye because the O.P noted that the color started a little green then got worse. That sounds like an algae growth pattern.
 

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