Dealing with black algae (Part 1 of 2)

My apologies for the long post but otherwise it is too hard to understand.

After having been a member of this forum for some time I now hope that I can give back to the community in the future. My two main personal areas of experience are iron stains and Black Algae, both of which can be major problems in Hawaii. Recently I installed a Salt Water Generator and while I am very happy with it (Pool Pilot Digital) I am not very experienced with it. I have learnt by trial, error, and experience. I am not a pool specialist but in these two areas my pool which was once a poster child for these problems is now free and clear. Those that visit our home think we have a new pool and often comment that it is one of the best looking pools they have seen – if only they knew.

The following I hope will help those of you with black algae with more than a few spots. Having lived both in Florida and now in Honolulu, Hawaii I have experienced a number of older pools, including my own, that are in various stages of delaminating, from minor plaster loses to major, and thanks to this forum have learnt how to deal with this issue. There may be other methods that I am not aware of but these methods have proven successful for me and those I have helped. Much/most of this knowledge was garnered from ”Chem Geek’s” postings, who might wish to correct or comment on this posting some of which may not be as accurate as I believe, I will take no offense and would welcome such constructive criticism. I have no experience with Fiberglass pools and cannot comment on them.

Method for controlling black algae in older delaminating PLASTER/CONCRETE POOLS ONLY:

Killing Black Algae:

Black Algae is thought to be a form of marine algae and loves to live in cracks. It has a thick outer membrane that cannot be broken by chlorine at normal levels (read near impossible). Main sources are swimming trunks that have been in seawater and not washed prior to entering pool, wind born debris blown up from beaches and carried over land and mountains, and dogs swimming in the ocean and not properly washed down – there are other sources. And because they come from the ocean they love salt water pools. There are at present only two methods for controlling with which I have had success. Note: Pouring Chlorine directly on it in a pool full of water does not work as it dissipates too fast and the membrane is not broken for long enough. These methods and calculation do not apply to those of you that do not have this problem.

Method One:

The membrane needs to be broken using a wire brush 3 times a day for at least 4 days, possibly 7 days. The pool would need a maintained shock level of 25 ppm chlorine to kill it for 4 to 7 days. This ideally should be done every 8 hours, and best of all every 6 hours. Hiring some local children during the holidays to do the scrubbing ONLY can reduce your manual labor at a reasonable cost. Kill rate varies with scrubbing effort.

Method 2:

An alternative method, far less labor intensive, and simpler, is to drain the pool so it is empty by nightfall. Then scrub the affected areas with a wire brush, or wet/dry 1000 grit sandpaper, and cover with towels soaked in pure chlorine in darkness (chlorine loses most of its strength in sunlight). One would also need to remove the lights from their sockets and soak the enclaves as it tends to hide in there. This works very well with a near 100% kill rate. Refill in the morning, preferably before sunrise and leave the towels in the pool, retreiving them after they start floating.

Note: To enhance this method a short acid wash of the affected areas with 1 part muriatic acid to 5 parts water (1:5) may help break down the cell wall. Wash off immediately with lots of water and then cover immediately with chlorine soaked towels.

Controlling Black Algae:

It can be controlled from growing (re-growing) if one uses a combination of all of the following method:

1. An initial dose of Algaecide 60 at 14 ozs per 10,000 gals. And then a maintenance dose of 3 oz per week per 10,000 gals.
2. Boron maintained at level of 50 ppm (Common Household Borax sold in 76 oz units) in the pool (a small replenishment is usually only necessary every 3 months). See the BBB method on this sight and the China Shop on how to do this. LaMotte has the best test strips.
3. A chlorine level to achieve an HOCL level of 0.075 or higher (HOCL levels are pH and CyA dependant so they need to be calculated to find the optimum chlorine value need to be maintained in the pool. HOCL levels below 0.075 cannot kill marine algae so it will slowly re-generate. My experience is that when the HOCL number falls below 0.075 black algae will very slowly creep back. You can download the excellent “Pool Solutions” Excel Spreadsheet here and play with your numbers:

http://richardfalk.home.comcast.net/pool/PoolEquations.zip

Or use Ben’s rough guide depending on your CyA level as follows for chlorine (use the higher max number):
Stabilizer CyA . . . . . . Min. FC . . . . Max FC . . . 'Shock' FC
=> 0 ppm . . . . . . . . 1 ppm . . . . . 3 ppm . . . . 10 ppm
=> 10 - 20 ppm . . . . 2 ppm . . . . . 5 ppm . . . . 12 ppm
=> 30 - 50 ppm . . . . 3 ppm . . . . . 6 ppm . . . . 15 ppm
=> 60 - 90 ppm . . . . 5 ppm . . . . . 10 ppm . . .. 20 ppm
=> 100 - 200 ppm . . . 8 ppm . . . . . 15 ppm . . .. 25 ppm

Why do some Salt Water Generators not kill off black algae?

Some salt water generators sold and purchased can be under powered. It is easier to sell to the public when the units are cheaper. This is especially so when they are sold by some less experienced or less than honest pool maintenance person as their clients would balk at having to pay for the proper sized unit as they are more expensive, also your pool person’s profit could be lower or you might think that person too expensive, become suspicious, and get yourself a new pool person, so it is partly us the general public to blame. It is akin to the old painters’ saying “What’s the most expensive paint job. Answer – The cheapest”. So it is with saltwater generators. One can always upgrade one’s unit to a larger size to generate more chlorine.

Note: Paint labelled "Professional Grade" is normally the lowest quality and the cheapest so study before you buy. But Professional sure sounds good!

Most units sold can generate 1-3 ppm chlorine and they do an excellent job of keeping the water clean and can control some other algaes; but to kill black algae the water would need to have a higher chlorine residue level as it need to sit on the algae at these levels to stop it growing more. So if your unit cannot generate 5 ppm of chlorine at a a CyA of 30 you will have a hard time contolling black algae.

The above chart from Ben illustrates the residue levels at which the chlorine needs to be maintained based on the CyA level (Note: Use the higher Max FC):

As most saltwater generators require a CyA level of around 60 ppm, one would need to maintain the chlorine at a level of at least 9 ppm and possibly 10 ppm. This is way beyond the capability of most under-sized Salt Water Generators, even some properly sized units.

Is Chlorine too high at 5ppm

The answer is no as its real strength is mitigated, controlled and measured by the affects of the CyA level. The higher the CyA the lower the killing power of the chlorine.

Part 2 of 2

What to do:

Method One:

Upgrade your saltwater cell to the largest available for your unit. Drop the CyA level to 30-35 and maintain 5ppm chlorine by powering your unit until it achieves that level. Run your pump so that it turns the water at least 1.25 turns (1 turn maybe ok). This is calculated by taking the size of your pool in gallons and dividing it by the flow from the pump in gallons per minute. You will need a “Gallons per Minute” gauge attached to your exit pool line. 20,000 gallons divided by 55 gallons (or 65/or 70) per minute (average for most pools – use this number if you do not wish to buy a gauge) = 363 minutes = 6 hours times 1.25 = 7.5 hours pump run time.

Method Two:

Do not buy an upgraded cell. Increase your SWG's output as high as you can without damaging it and calculate your Chlorine level generated by your Saltwater Generator add as much bleach to get it up to 5 ppm each day. Measure daily and add the necessary dose. 24 oz of WalMart’s bleach will raise a 10,000 gal pool by 1 ppm (allowing for loss of strength due to heat and light in transportation). This will be an ongoing daily task.

Method Three (for 2” Lines only):

Purchase a IntelliFlo VF High Performance Pump see here:
http://www.pentairpool.com/products/products3.php?id=77
Based on their energy calculator the pump should run 10 hours per day and save you around a $1,000 per year at 35c per KwH (Hawaii Prices). It will also allow you to run your Salt Water Generator Longer and then you might be able to achieve 5 ppm chlorine possibly even with a lower sized unit as chlorine is produced most efficiently at lower flow rates.

What Are Ideal Numbers Pool Numbers for a SWG with 4000 ppm Salt Content:

At 78 F At 84 F

Measured pH 7.5 7.50
Total Alkalinity (ppm CaCO3) 80 80.0
Free Chlorine (ppm Cl2) 5.0 5.00
Cyanuric Acid (ppm CYA) 30 30.0
Calcium Hardness (ppm CaCO3) 400 400.0
Total Dissolved Solids (ppm) 4,450 4,450.0
Total Borate (ppm Boron) 50.0 50.00
U.S. Gallons 10,000 10,000
Temperature (F) 78 84

Total Chloride Salt (ppm NaCl) 4018 4019.3
Carbonate Alkalinity (ppm CaCO3)64.0 63.3
Langelier Saturation Index (LSI)-0.13 -0.08
% HOCl (vs. Total Free Chlorine)1.5% 1.5%
OCl- (as ppm Cl2) 0.090 0.097
HOCl (as ppm Cl2) 0.077 0.077
Calcite Saturation Level (CSL) 0.53 0.59
Calcite Saturation Index (CSI) -0.27 -0.23

Why these numbers if ones salt level “Total Chlorine (ppm NaCl) is around 4000?

A pH of 7.5 is good for three reasons, firstly it is approximately the pH of the Human Eye so it avoids stinging eyes, secondly it helps keep metals such as iron in solution thereby not staining walls (any higher and stains will settle), and finally chlorine is more powerful at a lower pH.

Total Alkalinity at 80 or lower helps slow the quick rise of the pH therefore less acid is needed.

Two very important numbers to achieve are HOCL and CSI (You will need the afore mentioned PoolEquations spreadsheet to calculate these numbers).

HOCL should be maintained at above 0.075 to kill off and stop the spread of black algae. This can only be achieved if the pH (in this case 7.5) is matched to CyA of 30. If the CyA is any higher the HOCL level will be too low this is also true if the pH is higher than 7.5.

The CSI (Calcium Saturation Index) is important if you do not want your Salt Water Cell to clog up a lot with calcium, it will stop you having to clean it too often and prevent its early death. The important number here is to make sure it is around minus -0.20, or if you prefer very mildly acidic. With a pH of 7.5, alkalinity at 80, CyA at 30, and Calcium Hardness at 400, and Borate at 50, these numbers give a CSI in the -0.21 to 0.27 safely acidic range, which should reduce the maintenance on your salt cell but not strip the calcium off your pool walls.

If your SWG recommends a salt level of 3000 ppm here are the numbers:

At 78 F At 84 F

Measured pH 7.5 7.50
Total Alkalinity (ppm CaCO3) 80 80.0
Free Chlorine (ppm Cl2) 5.0 5.00
Cyanuric Acid (ppm CYA) 30 30.0
Calcium Hardness (ppm CaCO3) 375 375.0
Total Dissolved Solids (ppm) 3,440 3,440.0
Total Borate (ppm Boron) 50.0 50.00
U.S. Gallons 10,000 10,000
Temperature (F) 78 84

Total Chloride Salt (ppm NaCl) 3010 3011.3
Carbonate Alkalinity (ppm CaCO3)64.2 63.5
Langelier Saturation Index (LSI) -0.15 -0.09
% HOCl (vs. Total Free Chlorine) 1.5% 1.5%
OCl- (as ppm Cl2) 0.089 0.096
HOCl (as ppm Cl2) 0.077 0.077
Calcite Saturation Level (CSL) 0.56 0.62
Calcite Saturation Index (CSI) -0.25 -0.21

Notice the only change is the Calcium Hardness amount 375 versus 400 as one has less salt buffering at 3000 ppm.
A good simple online calculator to know how much to add or subtract chemicals is the Pool Calculator at:

http://www.poolcalculator.com/

It is not as precise as the “Pool Equations” spreadsheet for exact measurements but is fine for calculating chemical needs or subtractions.

Sorry forgot one cautionary issue.

If you do empty your pool remember to use Ben’s Calculator for CyA and add about 4 ppm chlorine initially (never over 5 ppm), and check twice a day to maintain it there; as the CyA may take 3 – 7 days to work fully. Otherwise you may get algae and not just the black kind. Also adding Algaecide 60 will help but it might drop your chlorine level.

It's interesting that the black algae is so hearty in your area. It might depend on the specific species. In lab studies by Sommerfeld & Adamson in 1980, Oocystis sp. green alga is the easiest to kill, next is Phormidium minnesotense (Tilden) Drouet black alga, and the hardest is Pleurochloris pyrenoidosa Pasher mustard alga. The chlorine inhibition level for the mustard alga was roughly double that of green alga and black alga was about halfway in between. Of course, they had the black algae free-floating and not adhering to plaster surfaces.

In most pools, having Ben's Min level of chlorine combined with weekly brushing keeps away black algae, at least as far as we can tell from reports on these pool forums. Your situation is (unfortunately for you) more difficult -- possibly due to the heartier local alga species. At least you've found a reasonable way to manage it. I assume you tried other less stringent methods with weekly brushing but were unsuccessful (i.e. the black algae would slowly return).

Richard

Chem Geek,

You are correct on both your assumptions. The black algae, more properly known from reading further, as blue-green or cyanobacteria, as far as can be seen, stays "glued" to the plaster and yes I did try the scrubbing method without great success. See article on it here maybe we can sell it to NASA to grow on the moon as described in external links at end of article.

http://en.wikipedia.org/wiki/Blue-green_Algae


So I suppose it must be made of stronger stuff. We have a saying here "Hawaiian Superman" maybe this is "Hawaiian Super Algae" and no I am not originally from here. The type tested in 1980 must be the "Weak Little Haole" type aimlessly floating around; true according to my wife. For information Haoles translate to puny white people, like me, originally the truer Hawaiian translation meant foreigner among other things, but nowadays it is used mostly as a joke and even as a term of endearment, although it can be derisive, as in "Stupid Haole", not very nice but it helps white persons like myself realize how bad and sickening racism is. Maybe we could sell your type as a pet!

A more complete description of the history of the word Haole can be found here:

http://en.wikipedia.org/wiki/Haole

Mustard algae has not been a real issue on this side, the south, of Oahu although I am told it can be prevalent on the North Shore, why I do not know.

After writing this I had a thought, would not the BBB method work better? It did work well for me for a number of years albeit time consuming.

For those of you that have the time, staying at home most of the time, the answer might be yes. But if you work or travel and your time is not always your own a Salt Water Generator is, to my mind at least, the way to go; it consistenly outputs the correct amount of chlorine.

If one has a digital controller for the acid (highly recommended) the daily tasks of checking can be skipped occasionally; giving piece of mind if one is unable to attend it, again for those of us whose schedules are controlled by others or events.

As always thank you for your reply and knowledge.

PS. If you have any scientist friends here let me know as I know of a pool that has a plentiful supply of the "glue" type. Why because he actually believes his pool person can get rid of it by diveing and scrubbing at $150 an hour! And yes he's a Haole, worse still he comes from the same country I do originally; and only 3 miles from where I lived. Please, please don't tell the Hawaiians, I don't want him and me to end up like Captain Cook.

See the 3rd voyage here:

http://en.wikipedia.org/wiki/James_Cook

I forgot to mention this earlier, but there is another option that may work for you regarding black algae (or any algae, for that matter) and that is to use a phosphate remover. It's a last resort, is expensive if you've got high phosphate levels or regularly introduced phosphates, but it does work. In some ways you can see this as an alternative to the weekly PolyQuat 60 (and the Borates, though those are just added once and inexpensively maintained), but could let you have lower chlorine levels. By the way, for the heck of it I bought a Taylor phosphate test kit and found that my fill water is more than 500 ppb in phosphates and my pool is well over 1000 -- I estimate between 2000 and 3000 ppb if not more. I'm able to maintain my pool with chlorine alone with no algae (except some green algae inside the skimmer above the water line, but never in the pool itself).

Richard

Chem Geek,

You might be on to something here about "Phosphate Remover".

A little while ago I did add phosphate remover and as I still had such a large bottle of it left I have been using a small dose of it once a week. It seems to help the ORP stay higher and more consistent. Some say because it is dirtying the filter.

I did not want to add that to my post as many persons feel that it is a "Snake Oil" remedy, which indeed it might still be. I too am beginning, however, to have a sneaking suspicion that it might actually be helpful, even though my original levels were far lower than yours on the test being over 200 but under 500.

Maybe we could get on the front page of the "Phosphate Remover Monthly" as originally skeptical converts. I'll call my agent about royalties, 50-50 ok with you?

Seriously I think that maybe something in it is not liked by what little black algae remains secretly hiding out in my pool and that is why the ORP is better and more consistent, although I feel the HOCL above 0.075 is the most beneficial treatment.

Like you I have green algae at the skimmer above the waterline but it is not a problem. Maybe we could invent "Skimmer Algae Remover" and retire!

SmallPoolDad:

Wonderful exposition! I learned a lot--and clearly your "Black Algae" is not the same species we see in the North Eastern states.

I learned:
1) Don't buy an old pool!
2) If you do, have wire brushes.
3) Don't keep a pool in Hawaii unless you want a lot of work--and if you do, make it vinyl!
4) Hawaiians are just like everyone else--they breed their share of bigots just like the rest of us.

Carl D,

Firstly thank you.

In response by item:

1) True, but as they get older at $8,500 in Honolulu a resurface it is hard for retirees on a fixed income. If one does get it done in Honolulu hire a good concrete engineer ensuring he is on-site to make sure the prep-work is carried out properly, the Portland cement's slump is correct (not too much water), good synthetic additives are used including artificial fibers to strengthen the mix, and then cured properly. No marble chips here.

2) Yes wire brushes are second only to chop sticks. They are even more important than having a cute little Thai or Korean girlfriend for us PoolForum aficionados; well maybe!

3) True, I think that vinyl replacements if purchased locally will cost nearly as much. But buying them from the mainland now that's an idea worth reviewing.

4) Yup, but having lived all over the mainland I think that this is better here. It is good to be in the minority it gives one a better understanding of others plight. And where in the world can you find 300+ lb guys (and girls) with muscles the size of SUV tires, tattoos all over, opening doors for you and saying "No you go first, you only got a few items" That's why I love it here. It isn’t just the cute Thai and Korean girls that make it a pleasure to live here. I swear on my black algae.

Aloha