Black marks on pool steps

I have an inground 16x32 vinyl pool. Water readings are:
FCL - 2.53
TCL - 2.65
PH - 7.2
ALK - 101
CH - 152
CYA - 22

The water temp is 88 and the water is very clear. My problem is that I have black marks on my fiberglass pool steps. They look like scuff marks you would get from a black sole sneaker. I cleaned off the steps with a Mr. Clean Magic Eraser and got all the marks off of them. Two hours later I see that they are coming back!!!

I'm trying to figure out what this is and how to get rid of it permanently.

Alan

I don't know. Maybe take a picture of it and either post it with flickr or picasa or something or email them to poolforum@gmail.com. Hopefully someone will be able to help you identify the black marks. Have you let your chlorine drop? It sounds to me like a type of black algae.


I can see that you are having your testing done at a pool store. Those readings are a give-away. There is no way to measure levels to that level of accuracy. You are better off getting your own test kit. We recommend the Taylor K-2006 but since it can only be ordered online, you need something to use in the meantime. So, for now, get a cheap OTO (yellow drops) / phenol test kit, or if available at YOUR Walmart (check availability), get the HTH 6-way DROPS test kit, which is compatible with the Taylor K2006. Test the pool as soon and you can, and post the results. If you get the 6-way kit, ALSO test the water you FILL the pool with, especially if it's a well, and post THOSE results as well. (The HTH is the best available kit you're likely to find locally, but it's not the K-2006. It can only provide rough measurements chlorine levels above 5 ppm, and it measures "TOTAL" hardness, rather than "CALCIUM" hardness, which is not ideal.)

It's much easier to answer your questions, when we know something about your pool. We often 'waste' the first few posts back and forth collecting information. So, please complete our new Pool Chart form -- it takes about 30 seconds, but will save much more than that.

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Welcome to the Pool Forum, by the way!

Thanks for the quick reply!

I do have my own test kit and test the water myself. I am using the ColorQ Pro 7 plus test kit. The measurements I posted are from using it. From the research that I did the feedback seemed to be pretty good on the ColorQ test kit as far as accuracy so I went with it.

I will take a picture and send it in to see if that helps identify the problem.

I will also complete the pool chart form as well.

Thanks!

Alan

That's a pretty expensive kit and you're right it did get pretty good reviews. (I wasn't familiar with it, so I looked it up.) The downside to it, though, is that it is a DPD kit and will not test high chlorine readings like the K-2006 will. Also, from what I could tell, there is not a CC (combined chlorine) test with that one which is also an important piece of information to have when you are fighting algae problems. Some reviews also suggested that the CYA test gives low readings and the calcium hardness test is not too accurate. Maybe ChemGeek or Waterbear will have information on this kit that they can share.

Hopefully, someone can help you figure out what those black marks are. Glad to have you here on the forum with us!

Never heard of anything like that. I'll see if Waste or Waterbear have.

I'd like to see a pic. Also, be aware that the magic eraser is a actually an abrasive pad and can damage the gel coat on your pool and make matters worse. Black stains are usually either copper or mangansese or an algae. Start with a full set of water test results done with your ColorQ (which, btw, while good, does have some limiitations compared to the the LaMotte 7022 FAS-DPD test or a Taylor K-2006)