Return Hose Turning Black

by Rachel

We hacce an above ground pool that has a salt water system. We've had this set up for 2 years now and have noticed this year that the return hose going from the salt water pump into the pool keep turning colors. It starts out clear and progressively goes from light green, to dark green and then to solid black! The other hose from the pool into the filter pump remains clear. Our pool water is still clear.

We are on our second hose now after the first turned black. After about a month this one has now started turning and is green again. I disconnected the hose from the port in the pool trying to figure out the problem. Black specks shot out from the port and the cap was caked in a thick black substance that could only be removed by scratching it off.

With everything else being crystal clear I can live with replacing hoses but I want to make sure this isn't ruining our salt water pump or worse, harmful to those of us that swim in it.

Thanks for the question Rachel

I'd like to have your complete chemical readings: chlorine, CYA, pH, alkalinity, calcium hardness, and any additives you've used such as flocs, phosphate removers, etc... Possible water problems start with the most recent and correct readings.

It does seem somewhat uncommon for good water to be going into the filter and bad water coming out. I would rule out black algae because that is mostly reserved for plaster pools. It can happen with vinyl but is uncommon.

kind of filter do you have? It's possible that the filter is disintegrating from the inside but you'll need to do a visual to confirm that. With a sand filter you may need to change the sand. DE filter, check the grids and replace if clogged, torn, or ripped. Cartridge filter would need to be replaced.

Let's say that good water is going into the pool pump and filter, then it's being returned as green and/or black water. Something is going on inside the filter or the pump basket that it causing this. It's kind of hard to say without knowing the type of filter you have and looking inside the filter to see what's going on. There could be something inside that's causing this issue.

There's also an issue with algae building up inside the filter. This is also uncommon but can happen from time to time. Normally green algae can be seen throughout the system, including the pool.

What you can do is open up the cap once again. Chip off a piece of chlorine tab and put in inside the hose. If the section fades or get lighter you have an algae issue and will need to take the right measures. I don't say shock right away because the chemical readings will tell us the course of action to take.

To post a reply, or if you have a similar question, you can see your post on the Q&A page in the "Black Algae" category.

Check back to this post for updates or answers.

Hope this helps and have a great Summer.


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How Much Is The Pool Service Responsible For?

by Karen
(Tampa, FL)

We've been using the same pool service for about 15 years. It's a weekly chemical service. We clean/vacuum the pool ourselves (admittedly not often enough). The pool is uncovered and uncaged.

We've had a lot of rain over the last few weeks and a couple of heavy storms. I could see from my kitchen window that the pool was very dirty from the last storm (it had been approximately 3 weeks since anyone was in the pool).

When I got into the pool on Saturday to vacuum, I was horrified to realize that under the dirt and along the sides of the pool, was a terrible infestation of black algae.

Would this have been prevented if our pool service had been adequately doing their job? Are they responsible for cleaning this up?

Thanks for the question Karen

We moved to Palm Harbor from Oregon in January and I was just in Tampa today for another appointment.

Anyway, even with the best pool care and maintenance you can get black algae, not likely, but it does happen. I've never had it in my pools on my route in Arizona, but I've received calls from pool owners that had a black algae problem and cleared it up for them.

Black algae just doesn't appear overnight, it does take some time, especially when you have a very large infestation. It can and will adhere to anything it can get a hold of.

It would be great to have a complete list of your readings. This way I can make an educated decision and see if the readings are off. Hopefully they aren't.

Here are some of the main reasons why your would get black algae:

  • Low or inconsistent chlorination.
  • High pH, above 7.8. Anything over 8.0 and you're only using about 25% of the chlorine. 7.4 - 7.8 is what I recommend.
  • High/low pool stabilizer/CYA. The CYA range is 30 - 50 ppm. Low is 20 ppm or lower, and high is 70 - 80 ppm and above. Each one of these will cause the chlorine to be less effective. The main reason for chlorine is to kill, period. It kills the organic matter and bacteria.
  • Inconsistent alkalinity. The range is 80 - 100 ppm, 120 ppm being the top. If the TA is not locked in you're going to get pH bounce which means just that, the pH is not consistent, which in turn can cause the chlorine to be less effective.
  • Poor circulation and/or not running the pumps enough.

    This is why having the readings are important. If the CYA is too high then the chlorine can't do its job. If it can't work then you're going to get algae.

    If the black algae is visible even with dirt in the pool (the question states there's black algae on the walls of the pool) then I'd say that the pool company is responsible for the algae problem.

    But, if the pool was so dirty, all the time and each time he went there on a weekly basis, that a reasonable person couldn't see the algae through the layers of dirt, then that's where it gets dicey. He could simply say, "I'm there to keep the water balanced and couldn't possibly see the black algae because the surface was so dirty". But I think that's stretching it a bit. What you're dealing with, in my opinion, is a possible "shared responsibility" or "shared agreement" status. I had a few "chemical only" pools on my route.

    To the best of my knowledge, black algae isn't a result of a semi-dirty pool. It's more of a result of poor pool water maintenance so I would say the pool company would need to carry the burden of making it right for you and clear up the black algae issue. Some say that black algae must be introduced into the pool through bathing suits that have been in the ocean but I haven't seen any definitive evidence for that. If the pool was at least clean enough to see the surface, and the black algae growing, they should have been proactive in telling your earlier. Again, this isn't an overnight "surprise I'm here" kind of algae. It takes time, sometimes weeks, to grow into an infestation.

    To post a reply, or if you have a similar question, you can see your post on the Q&A page in the "Black Algae" category.

    Check back to this post for updates or answers.

    Hope this helps and have a great Summer.


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    Black algae in Doughboy vinyl liner- stains clear then come back?

    by Charles
    (Wilton, CA)

    I used test with 3" tabs for black algae. Treated which cleared up very nicely then in 24-48 hours came back with same pattern "stain". Is there a way to get rid of it permanently?

    Hi Charles. Black algae is not very common in vinyl liners. Black algae has legs, or tentacles, that dig into the surface. Normally, this can only be accomplished in a plaster or concrete pool. Vinyl is just too shallow and slick for it.

    But it can happen. If your pool truly has black algae, the only remedy is to maintain a high FC of 15 ppm for a few days, scrub the liner down with a nylon brush and treat the affected areas with chlorine tabs. Keep filtering and backwash once per day for 3 - 4 days.

    It called "the herpes of pools" for a good reason. You can try to contain it, but you can't control it. Once it's in there, it's in. You never know when the next outbreak can occur. It could be next week, or 2 months from now.


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