Black/Brown Spots On Bottom Of The Pool As Well As In Grout Lines Of Tiles

by Amy

Initially we had a slight green/yellow tint to the pool with brown looking debris that when swept would cloud up the pool but most of it would not budge. We cleaned the filter, backwashed, and ran the filter. A week or so later we did the same thing again (mainly because when we cleaned the filter the first time we found one of the grids was broken so we were replacing it). I believe at this time my husband put chlorine in. After that the pool cleared up a lot and now we are left with these black spots on the bottom. In between the tiles in the grout lines are clumps of black and around our rock water feature is a black line where the water level is.

The pool store said to add a conditioner (half bottle - Natural Chemistry Instant Conditioner) run the filter all night, back wash and then test the water again. Here are the chemical readings after adding conditioner and running the filter all night: FAC: 5 TAC: 5 Salt: 4400 CYA: 60 TA: 120 pH: 8.0 Acid Demand: 2 Copper: 0 Iron: 0 Phosphates: 200 Can you help us get this black/brown areas cleared up and the phosphates down? We have a D.E. Filter and 13,000 gallon pool.

Thanks for the question Amy, and for the readings. It makes life so much easier.

First thing is to NOT put any more conditioner/stabilizer/CYA in the pool. The CYA range is 30 - 50ppm and you're right at 60ppm which is high normal. I have no idea why the pool store employee told you to put conditioner in the pool. That's specifically to help keep the chlorine in the pool longer. Only if your CYA is below 20ppm would you want to add conditioner.

You can do a very simple test to determine what kind of stain you may have. Get a
chlorine tab and put it on an affected area for a couple of minutes. If the stain lightens up it's organic and can be removed using tabs and shocking the pool. I assume you're on city water which doesn't have metals so I'll rule that stain out. It may be black algae in which case you can only ry to contain it. You can't completely get ride of it because it digs into the plaster. Scrape the heads on then scrub with a wire brush. Once that's finished scrub the areas again with a chlorine tab, shock the pool, then add a thin layer of Trichlor chlorine to the affected areas. You need to first get the pH down to 7.0 - 7.2 before you shock. Chlorine works better at this pH level. You'll use 1 gallon of liquid chlorine for your size pool and with the current FC level.

Don't be concerned in the least about the phosphates. It's just another way for you to spend money on your pool that you don't need to. Yes, phosphates are food for algae but the chlorine already kills the algae faster than it can reproduce. Phosphates are fine to swim in and cause no harm to you nor your equipment.

You can first try to scrub the areas with a wire brush and a chlorine tab. It's going to take some grunt work. My pool route was in Mesa/Tempe so I'm very familiar with these kinds of issues.

If you feel your situation is more complex than this, I do phone consultations for a donation of your choice. It makes things go much faster and many people have found it extremely beneficial, saving them time and money in the long run. All your questions will be answered. I have nothing to sell you so you know I'm not bias.

Pool Consultation

Hope this helps and have a great Summer.


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