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2 Responses to “What Is Black Algae And How Do Get Ride Of It?”

1. windance says:

   July 1, 2009 at 3:42 pm

   First of all you must determine if it is indeed black algae. Do this by running rour finger across a patch of it. Use a good amount of pressure. Black algae feels slimy and will smear, leaving a “pencil streak”. If it is black algae it is troublesome, but not impossible to get rid of. First off, though, you have to mend your ways. Black algae grows because of neglect– a pool mans BEST friend! Watch those chemicals carefully and keep them topped off. Now that you’ve been chastised, here’s what to do.
   Check and adjust pH and total alkalinity. (Run the pump round the clock for a couple days throughout this process.) Shock the bejeebers out of the pool. Next morning add an algaecide formulated for black algae. My pick is silver algaecide. A bit pricey, but we need to do a lot of work here. Add the algaecide per label instructions– usually so many ounces every few minutes. DO NOT pour it all in at the same time! Cheap algaecides are not nearly as effective. You might be all summer getting rid of the nasty stuff.
   You didn’t specify if your pool is fiberglass, vinyl lined, or plaster finish. If, and ONLY if, it is plaster, brush the spots daily with a stainless steel algae brush. As black algae dies the gelatinous coating (which makes it such a difficult algae to kill) hardens into something rather like concrete. You’ve gotta “scratch” through this layer to expose the next layer down. (Effectively “unstacking” the layers.) After that is accomplished- if the pool is a plaster finish- swim down and feel all the little spots. You will notice dimples. These are trouble! Black algae (actually it is a blue-green algae) grows down into the pool finish as well as up. These dimples are tiny little hiding places for the algae to lay dormant. And you will always have a problem with black coming back to these same areas. Why? Because these “dimples” have a rough surface. The surface tension of the water will help keep chemicals out of the tiny holes. Hence, black algae can get a toe hold and come back as soon as you let the chemicals get out of hand. Use wet/dry sand paper to “feather” these areas. Take away the algae’s hiding places. That’s it in a nutshell. Keep those chemicals balanced. You have a pool 365 days a year, whether you ever swim in it or not! Be humane to the pool and maintain it!
   If you determine it is NOT black algae, we’ll discuss that in another post.

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2. nrsebone says:

   July 1, 2009 at 3:42 pm

   Perhaps the most aggravating strain of algae, it has been compared to herpes; “once you’ve got it, it’s there for life”. This is not entirely accurate, but the difficulty in eradication is due to the strong roots and protective layers over top of the black algae plant. Black algae will appear as dark black or blue/green spots, usually the size of a pencil eraser tip. Their roots extend into the plaster or tile grout, and unless the roots are destroyed completely, a new head will grow back in the same place. The heads also contain protective layers to keep cell destroying chemicals from entering the organism. Like yellow algae, black strains can bloom even in the presence of normal sanitizing levels and proper filtration. I was once told that this form of algae commonly enters a pool inside the swimsuit of a person who’s recently been to the ocean.
   First off, balance your water, paying particular attention to pH. Secondly, check your filter system and clean if necessary. Adjust valving for optimum circulation and allow it to run 24 hours a day until the pool clears. Turn on automatic cleaners to help stir things up. Backwash as necessary.
   For suspended green algae, shock the pool…hard. Put in as much hypochlorite as it takes to turn the pool a cloudy, bluish/gray color. Brush the walls and floors towards the main drain. Backwash the filter when the pressure gauge indicates the need. Using a flocculent may be a good choice if the pool is extremely “swampy”. If you cannot see the bottom of the pool, and it is filled with leaves and debris, it may be wise to drain the pool, acid wash and refill it.
   After the chlorine level has come down below 5 ppm, add an algaecide and brush the pool again. When it all settles, vacuum the pool (to waste, if possible). Check and rebalance the pool water if necessary.
   For algae which is not suspended, but only clinging to the walls, follow the same advice above, first shock with brushing, then add an algaecide, brush again, vacuum to waste (preferred) or vacuum and then backwash the filter. Use of a steel bristled brush is recommended for algae on plaster pools (use nylon brushes on vinyl). Filter, Filter, Filter.
   For black algae, the brushing part is very important. You must tear through the protective layers so the chemicals can destroy the plant from the inside out. Pumice stones work well to knock off the heads of black algae. (Don’t forget to vacuum them up later, and backwash them out of the filter ASAP). Also effective on the black algae nodules is sprinkling granular trichlor over the spots (of course if they’re on the wall this is next to impossible). Rubbing the spots on the walls with a trichlor tablet or stick can also be effective to knock off the heads and get trichlor directly to the roots. Follow up with a dose of copper algaecide, or high strength polymers. Simazine, an herbicide, was a very effective black algae treatment, but is no longer available in America.
   If algae has been an ongoing problem in your pool for several years, you may do well to drain the pool. Many years of algae builds up dead algae cells and lots of other solids in the water that contribute to its rejuvenation. Acid washing and/or pressure washing is preferable once drained, to kill the roots of the algae embedded in the plaster. NEXT: change the sand if you have a sand filter or change the cartridge if it is a cartridge type. Sand should be changed every 5-7 yrs (or every 2 if you use baquacil), and cartridge filters should have new elements every 1-2 years. If you have a DE filter (good for you!), you should remove the elements, spray clean, soak in a 10:1 water/bleach solution, rinse and replace. A well functioning filter will prevent algae.
   Another item to look at is the method of sanitation and the type of filtering you have. Far too many pools out there were sold with marginal filter systems, meant to run 24 hrs per day. Well, these systems get old and tired, or the new owners only run it 12 hrs per day (or less). For good algae prevention, we need a combination of good filtration, sanitation and circulation. It may be time to consider changing the old pump and filter. It’s cheaper and easier to pay a little up front for more chemicals, electricity or better equipment than all the money and aggravation spent on fighting algae blooms.

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