Is Alum Floc safe to use for metal stains?

[JenMichelle]

Alright TFP family, I'm at it again with my metal stains. So... I have been battling these ALL summer, and it's been hard to keep chlorine above 2 or stains come back. I haven't had to SLAM all summer but noticed some pink slime by my stairs and my water got a TINY cloudy, I'm assuming from low Cl, so I removed stairs and brushed the pool like crazy and am now slamming. Here are my results:

Cl 13
CC 0.5
Ph 7.3
Cya 30-35
TA 80

So I started the SLAM yesterday afternoon, and my water went from beautiful (minus the slight cloudiness) to a CRAZY deep green after I added the bleach.

Is that normal during the SLAM process?

At first I thought it was the stains sticking to the liner with such a high Cl level, but this morning I woke up and it was much lighter, and my Cl went from 12.5 overnight to a 5.5 this morning! So I am still slamming and the water looks great now, except for the slight metal stains on the liner.

I went to the pool store (they had liquid chlorine on sale) and got to talking to the owner about my battle with my staining. He suggested the brand EZ Clor "Alum Floc" which says its aluminum sulfate. He said this will get the deeply embedded metals out of my sand filter, which is probably the cause of the re-occurring stains. Whatcha guys think? Is it safe to use?

Is it possible that my staining isn't staining at all but algae? When I do the AA treatments the liner gets gorgeous, but when I slowly raise Cl over 2-4 ish they come back. I have also used the sequestrants as well. I appreciate any help! You guys are always awesome

 

[chem geek]

The alum floc won't get anything out of a sand filter. It's the opposite. What he was probably trying to say is that if you shock with chlorine to get to your green and then use an alum floc, that you may be able to filter out much of the iron from the water into your sand filter at which point you can backwash to remove it from the filter. In theory, you could just add DE to your filter when your pool has the dark green stage, but it's up to you. There are also some metal sequestrant products that claim to filter out the iron and not just hold it in the water, but we haven't found consistency with these.

 

[JenMichelle]

So do you think when I'm done slamming I should do my AA treatment, THEN add the alum Floc, then backwash after it grabs the metal?

 

[chem geek]

No. If you do an AA treatment, that turns the ferric iron that didn't precipitate into ferrous iron that is soluble so that it can get caught by metal sequestrants. The alum floc won't touch either of these ions -- they are both positively charged and will repel each other. The alum floc is only useful for neutral or negatively charged particles so would help consolidate iron oxide.

So if you want to try the alum floc (and your chances of success are dubious with this) then use it after shocking and see if it reduces the coloration in your pool and gets caught in the filter so when you backwash it looks like you're removing iron. It's after such removal that you could then deal with any existing staining using an AA treatment followed by use of a metal sequestrant. What will be tricky is that alum floc works best at lower pH, but the precipitation of iron happens from shocking which raises the pH. Again, sounds pretty dicey to me.

There are other ways you may be able to remove iron physically from the pool, though nothing has been shown to be foolproof. Some people report OK results using CuLator, but its not consistent and its a pretty expensive method.

 

[JenMichelle]

Thanks chem geek! I don't think I will risk using the alum floc, I'm afraid it will throw something else out of whack and cause more harm than good.