Algae growing with sufficient FC levels

Pmchick

Active member
Mar 13, 2010
40
Hello,
I have algae growing on my stairs, and various cracks in my pool. The FC is currently at a 2.8ppm & the TC is 3.9ppm
pH: 7.4ppm
This is an indoor swiming pool and the FC does not dip below 2.0ppm

I treat the pool once a week with Pool Perfect-Phos Free and I see no change. I brush and brush and in a few days, it is back. It appears to be black algae because in certain areas of the plaster, it grows in quarter size circles on flat plaster. The algae on the stairs and in the crakcs is green.

Thank you for your help :)
 

JamesW

TFP Expert
Mar 2, 2011
16,752
Since you have algae and CC (Combined Chlorine), you need to shock until they are both gone. What is your cyanuric acid level?

Also, forget about phosphates, they are not an issue.
 

chem geek

TFP Expert
LifeTime Supporter
Mar 28, 2007
12,083
San Rafael, CA USA
This is a large 126,000 gallon indoor pool with a retractable roof and the algae problem was also described in this thread. With the very high CC, there needs to be more exposure to UV in sunlight (or a supplemental UV system). I suspect the bather loads in this pool are rather high. Note that if any non-chlorine (MPS) shock is used, then that will register as CC in the chlorine test.

I don't know how accurate the LaMotte ColorQ system is for the CYA test. I'd double-check it against the Taylor test that we know to be more reliable, though still not an easy test.

Given the size of this pool, I strongly suspect that the circulation is very poor in some areas so local chlorine levels in such areas can get low, especially under conditions of high bather load that can use up a lot of chlorine (especially urination -- such as if little kids use the pool).
 

Pmchick

Active member
Mar 13, 2010
40
Today's readings:
FC: 3.2
TC: 3.8
CC: .5
pH: 7.4
Alkalinity: 112
Calcium Hardness: 311
Cya: 0-its a commercial pool and NJ law states that you cannot use CYA in a public pool.

I suspect poor circulation in these areas as well...there are no returns anywhere near where the algae is growing. THe returns cannot be adjusted They are the Hayward Grated Returns, there is no eyeball. Perhaps if I change the return fittings, maybe that will also help with prevent the algae after I shock it?

THank you,
 

chem geek

TFP Expert
LifeTime Supporter
Mar 28, 2007
12,083
San Rafael, CA USA
Well, with poor circulation and high bather loads consuming chlorine locally, you're only other real option is to use something in the pool that specifically prevents algae growth, but won't get used up by bather load, sunlight, etc. Unfortunately, that's going to be expensive due to the size of the pool or will have side effects.

For example, PolyQuat 60 is an algaecide that could be used, but must be added weekly so that can get somewhat expensive, though not terribly so -- around $130 for initial dose (for a 126,000 gallon pool) when algae is present and around $25 per week thereafter. A regular linear quat algaecide would be about 1/3rd the price, but can foam and is not always as effective against algae. At least the PolyQuat also acts as a clarifier so you get some of that benefit as well. Copper ions would mostly be a one-time cost, but could cause staining if you don't carefully monitor their levels and keep the pH from rising too much. 50 ppm Borates wouldn't have the staining side effects, but for a large pool would be quite expensive (about $500 initial dose and then weekly make-up for water dilution at some percentage of that) and I'm not sure if commercial/public pool regs allow it (I'll bet they're silent on the subject). The use of a phosphate remover would probably be at least partially effective, but would be very expensive if phosphate levels are high. So not great options here and these are just band-aids for the core problem which is poor circulation.
 

JamesW

TFP Expert
Mar 2, 2011
16,752
What more can you tell us about your system and operations? Algae should not be growing with sufficient FC levels.

I know that cyanuric acid is not allowed in indoor pools, but have you actually measured to make sure that the level really is zero? Since you have a retractable roof, which will expose the pool to the sun, you could probably get a waiver on the cyanuric acid.

What pump and filter do you have?

What is your flow rate?

What is the bather load?

What is the water temperature?

When was your last health inspection?

Were there any deficiencies noted by the health inspector?

When was the last microbial analysis performed, and what were the results?

I don't think that poor circulation in certain areas is a likely cause as long as you are maintaining the proper turnover rate. The required flow rate for your pool is a minimum of 263 gallons per minute. Are you achieving that flow rate? I don't see how any local area could be as much as 1 ppm different from another area for long as long as you are getting the minimum 8 hour turnover rate.

There is some critical information that we are not getting. The more you can tell us, the better.
 

chem geek

TFP Expert
LifeTime Supporter
Mar 28, 2007
12,083
San Rafael, CA USA
See this post for a picture of this 126,000 gallon pool.

If you were able to invert a sample tube and turn it over after putting it down in the area with algae, then you could measure the chlorine levels in that area. That would more definitively tell us whether circulation was indeed an issue.
 

JamesW

TFP Expert
Mar 2, 2011
16,752
Perhaps it's the glare, but the water in the picture does not look very good. It looks cloudy and hazy. I think that there is probably an issue with the filtration system and/or the chemistry.

Based on the previously reported TA of 130, calcium of 280, temperature of 86 F and if the pH got to 7.8, then the CSI would be + 0.53, which could begin to cause scale and calcium carbonate clouding.

I suspect that the FC levels have probably gotten too low (perhaps even zero) on occasion. Some operators are reluctant to report chemistry that is out of range for fear of getting in trouble and they report in a number that is in range.

With the reported number of kids using the pool, it would be easy for all of the FC to become combined with ammonia and urea. If the roof is open, then the sunlight could deplete the FC fairly quickly.
_____________________________________________

I think that the CO2 is completely counterproductive. It just converts hydroxide into bicarbonate, which raises the carbonate alkalinity. It's the hydroxide that raises the total alkalinity, but the CO2 converts it into a more problematic form of alkalinity. The hydroxide raises the pH and the TA, but the CO2 only lowers the pH, not the TA.

CO2 + OH- <> HCO3-

Adding muriatic acid then converts the bicarbonate into carbon dioxide and water.

H+ + HCO3- <> CO2 + H2O

Using hydrochloric acid would be a better choice because it converts hydroxide directly into water, which lowers the pH and the TA.

H+ + OH- <> H2O

Therefore, the carbon dioxide only creates unnecessary cost and complexity without any benefit whatsoever. You still need to add the exact same amount of acid to offset the TA rise from the hydroxide in the liquid chlorine.
___________________________________________________________

If the retractable roof is open for extended periods of time, then the sunlight could deplete the chlorine fairly rapidly with no cyanuric acid. If the roof is going to be open for any length of time, then it might be worthwhile to apply for a waiver of the "No cyanuric acid" rule for indoor pools, since the pool is technically not strictly an "indoor" pool.

8:26-1.4 Waiver
(a) The Commissioner or his or her designee may, in accordance with the general purposes and intent of N.J.S.A. 26:4A-1 et seq., and amendments thereto, waive sections of this chapter if, in his or her opinion, such waiver would not endanger the safety or health of the public.
(b) Any agency, organization, or entity seeking a waiver of the standards in this chapter shall apply in writing to: Consumer and Environmental Health Services New Jersey State Department of Health and Senior Services
PO Box 369 Trenton, NJ 08625-0369
(c) The written application for waiver shall include the following:
1. The nature of the waiver requested;
2. The specific standards for which a waiver is requested;
3. The reasons for requesting a waiver, including a statement of the type and degree of hardship that would result upon full compliance;
4. An alternative proposal which would ensure public safety; and
5. Documentation to support the waiver application.
(d) The Department of Health and Senior Services reserves the right to request additional information before processing an application for waiver.
http://www.state.nj.us/health/eoh/phss/recbathing.pdf
____________________________________________________________

Based on the bather load, it might be necessary to use some sort of supplemental oxidation process, such as ozone or UV.

Based on the ongoing issues, I think that it would be best to have a qualified expert review all operations and advise the pool owners/operators as to what is being done correctly and what needs to be changed. The continuous growth of algae indicates a serious quality control problem.
 

JamesW

TFP Expert
Mar 2, 2011
16,752
You might want to consider converting to bromine by adding 40 pounds of sodium bromide and then continuing to use the liquid chlorine to oxidize the bromide into bromine.

I think that you should consider closing the pool until the maintenance issues have been resolved.
 

chem geek

TFP Expert
LifeTime Supporter
Mar 28, 2007
12,083
San Rafael, CA USA
I must be missing something since I don't understand how converting to a bromine pool is going to help this situation. Also, that's very much a fairly permanent decision since going back to chlorine requires a complete drain and refill which seems very impractical with this huge pool. Finally, as a commercial/public pool, I'd much prefer chlorine over bromine since the brominated disinfection by-products (such as trihalomethanes, THMs) are more carcinogenic/mutagenic than the chlorinated THM (i.e. chloroform).
 

JamesW

TFP Expert
Mar 2, 2011
16,752
The roof is retractable, which will allow in sunlight, but they are considered to be an indoor pool and are not allowed to use cyanuric acid. Bromine would be more stable in sunlight conditions than unstabilized chlorine.

For any given pH, the percentage of hypobromous acid will be higher than that for hypochlorous acid.

Also, bromamines are much more effective than chloramines due to the monobromammonium ion.

Reference

One disadvantage to going to bromine would be that the bromine is limited to 4 ppm, which is a lower molarity than 3 ppm chlorine.

I think that they should apply for a waiver of the "no cyanuric acid in an indoor pool" rule, or ask to be classified as an outdoor pool. An outdoor pool can go to an FC of 4.0 ppm.

At any rate, I don't think that we are getting sufficient information to make a proper assessment.
 

Pmchick

Active member
Mar 13, 2010
40
Hello, everyone, thank you all for the useful information, I apologize for the delay, here are the specs of this pool.

I have the following:
126,500 gallon indoor swimming pool with retractable roof
3 TR140C sand filters-filled with Zeosand(just replaced a few months ago)
3 Pentair Whisper flow 1.5hp pumps
My flowrate is 325gpm
Bather usuage is around 70 people/day
We do recieve a bacterial test weekly, and we have been passing every week
THe health inspector has not been there since September


THe water in the picture looks cloudy because there was snow around and on the roof of the pool, but, the water was clear than. The water is always clear, there's never even a haze to it.
This pool was originally bromine when it first opened 8yrs ago. It was swtiched over to chlorine 4yrs ago(I inherited this pool about a 1.5yrs ago). From what I was told, the bromine used to cause rashes and sinus infections in many of the swimmers.
Would it be best to bring my FC up to 30ppm in order to kill the algae? The FC level has not dropped below 1ppm in about 6 months.

Thank you,
 

JamesW

TFP Expert
Mar 2, 2011
16,752
The problems with bromine were probably due to high levels of DMH (dimethylhydantoin), which is similar to cyanuric acid in its effect on bromine. The DMH is part of the bromine tabs (similar to how cyanuric acid is part of trichlor tabs). I think that bromine tabs should not be used due to the DMH.

Was the pool drained and refilled to switch from bromine to chlorine? If not, then you might still have bromide and dimethylhydantoin in the water, which might be part of the problem. The chlorine might be converting the bromide to bromine and then the bromine would combine with the DMH and you are not getting enough sanitation.

If the pool was not drained, then you should have the water tested for bromide and dimethylhydantoin. This can't be done at a pool store. You will need to find a lab that can do these tests.

You should test the level of cyanuric acid to make sure you know what it is. Don't just assume that it's zero. Then bring the chlorine up to shock level for your cyanuric acid level. Bring it to 10 ppm if there really is no cyanuric acid. Hold at shock level until the chlorine loses less than 1 ppm overnight and all algae is gone.

I would keep the pool closed until the water is clean, clear and chemically balanced.