Are these iron stains?

[Frodo]

Hello everyone. I have an above ground oval pool with a vinyl liner with a DE filter. I switched to the TFP method about 3 years ago. Prior to the TFP method, I was constantly fighting algae and shocking the pool with bags of shock from the pool store at least every week. Now that I've taken control of the pool, it's been mostly Trouble Free™. My question is regarding stains observed on my wedding cake stairs and on the liner itself. I noticed them last year but cleaning the stairs removed the stains. But now I see them again and I decided to see what the stains are. I tried the crushed vitamin C tablet and sure enough it removed the stains from the stairs (see pictures).

I also purchased the Taylor iron test kit and it showed 0 ppm in the pool water. I fill the pool water with municipal water which is sourced from surface water, so I wasn't expecting iron coming from that. I'm at a loss as to where I could get the iron stain, unless it's not really iron. The only odd thing I use that could be contributing are the drainage stones I put in the cylinder in the stair weight. I'm closing the pool on Saturday so I'll address the staining in the pool in the spring. I don't have a heater which could cause copper staining and I have borax in the water @ 50 ppm (if that's important).

Does anyone have any clues as to what I'm dealing with?

The stones look like this:


Stairs after vitamin C tablet

 

[pabeader]

I have an oddball question. What color is the dirt around your house and pool?

 

[Texas Splash]

I'm no expert on the stones or aggregate being used, but for the iron testing, you might consider testing the source water and not testing the water already in the pool (chlorinated). Once chlorine precipitates the iron in the water, the test may be faulty, so it's best to test the source before any chlorine hits it. That doesn't help with the stone issue, but should confirm the municipal water is iron-free. I suppose next year you could try a difference method of weighing-down the steps to see if there is any difference between the new method and the stones from before?

 

[Frodo]

Thanks for the replies. There's no exposed dirt around the pool. Surrounding the pool is pea stone and beyond that for 2/3 of the pool is a patio and grass for the remaining 1/3. I'll test the water from the outdoor faucet I use to fill the pool after work today.

 

[pooldv]

It sure looks like iron staining and the Vit C test backs that up. It could be from a low level iron from rocks, we've seen that before. It could also be from a low level of iron in your fill water. Iron will build up over time. Consider capturing rain water or diverting gutters to the pool for a iron-free source of water to replace evaporation and splash out. More here, Pool School - Stains in Your Pool

 

[Frodo]

I tested my fill water and no iron registered on the test. So I'm leaning towards the rocks I have in the weight in the stairs. Next spring I plan on addressing the staining in the pool. Does this sound like a plan? Upon opening and adding enough fill water, I'll make sure the pH is ~7.2. Then start adding ascorbic acid 1/2 lb at a time until the stains disappear. At this point, would I need to use a sequestrant like Jack's Magic The Pink Stuff? Would using a product like CU Later help and would I need to use the pink stuff with it or not?

Thanks for the help guys. This forum is great.

 

[pooldv]

If the source of the iron is the rocks then the best course of action would be to do the ascorbic acid treatment to life the stains and do a partial drain to remove the iron from the pool. Then you won't need to use a sequestrant or CUlator. With a vinyl liner pool be sure to leave a foot of water in the shallow end when draining to prevent liner shrinking and shifting.

You can add your pool info to your signature so that we can better help you. More here, Pool School - Read This BEFORE You Post

 

[Frodo]

I opened my pool this weekend and decided I would attempt to tackle the iron staining. I opened on Sunday, May 14 and the water looked pretty good. It even had 3 ppm of chlorine left (I closed with 12 ppm). pH was 7.2 and my TA was 70. After adding some water and starting up the filter, my CYA was 30. When I first started with the TFP process 3 years ago, my CYA tested over 100 from using tablets. To take care of the metal stains, I followed this thread http://www.troublefreepool.com/threads/2129-Ascorbic-Treatment-to-rid-Pool-of-metal-stains.

I started by placing a CuLator Ultra PowerPak 4.0 in the pump basket, adding 1 lb of ascorbic acid and brushing to help mix. In about 10 to 15 minutes, the brown stains on the liner, return jet, skimmer and weir flap were gone. I waited 15 more minutes for things to mix well. I wanted to find out how much iron was in the water and since it's now in solution I figured I would try the Taylor iron test kit. However, that still showed 0 ppm. I added some Jack's Magic The Pink Stuff and let that circulate as I brushed again. On Monday morning I checked the pH and chlorine. Chlorine was zero, the pH was at 6.8 and the TA was still at 70. I added some borax to bring my pH back up to 7.2. When I got home from work, I checked the chlorine, pH and TA again and they were the same. So I added some bleach to bring my chlorine to 4 ppm and vacuumed and brushed the pool. I checked after and needed to add a little more chlorine to bring back to 4 ppm. I then used the iron test kit again and it still shows 0 ppm. This morning before I went to work I checked the chlorine, pH and the iron test. Chlorine was at 3 ppm and the pH was holding steady at 7.2. Still the iron test doesn't show anything so I'm not sure what's going on with that. I hope the CuLator product will work because I'd rather not drain the whole pool.

The next step is to clean up the stains the wedding cake stairs and swap out the rocks in the weight for some sand. Here's some pictures I took yesterday after vacuuming and brushing. The water looks great but it's really cold.