manganese precipation

[lews]

I'm on well water on an old gold mine parcel in NC. The original fill was from a reservoir and top ups are from the well filter through iron filters. I also adjust ph slightly trying to maximize the efficiently of the filters but still have pool staining. Even with the filtering, the water testing (by the county) shows high levels of manganese. Here's the odd thing. FYI - I have sequestrant in the water Jack's purple. When I top off I usually get what looks like the beginning of a algae bloom, so I shock and bam, the pool turns green - just like an algae bloom that I didn't catch fast enough. This year, for example, I notice the pool starting to have a hint of green, and with the water being to cold for the generator and us having some warm days, I thought it wouldn't hurt to hit it will some bleach. Bam, what looked like a bloom, even though the water is in the 50s. No way, right? So i clean the filter (paper) and it is slam full of this brownish film. I can wash it off but is takes a brush.

As soon as I have the clean filter back on-line, the pool quickly clears.

Do you chemistry folks think I'm precipitating manganese enough for the filter to catch it? And if so, would it make sense to repeatedly shock the water in order to get the manganese from the water? The staining on the pool is not terrible but not great either. It looks like iron staining, but doesn't come off with Vitamin C and Jack's test shows clearly it's manganese.

Thanks for any help.

Lewis

 

[JoyfulNoise]

Do you know what the manganese levels are in the fill water? Manganese and iron often are found together due to the minerals they are derived from so your “green” water is likely due to iron oxidation (yellow iron oxide + blue water = green hue).

 

[lews]

I do have iron as well but I think that's managed by the greensand whole house filter and the staining doesn't come off with ascorbic acid or Jack's stain test, so i think the staining is actually manganese. The county test of the well water (not the pool) showed iron less than 0.05 but manganese at 0.450. I also have a iron test kit and it shows very low levels of iron in the pool.

- - - Updated - - -

By the way, I have a house water from 10 years ago (before I installed the whole house greensand filter) and it showed iron at 1.33 and manganese at 0.39.

 

[JoyfulNoise]

Yikes! That’s a lot of manganese. I believe 500ppb (0.5ppm) is the EPA limit before water has to be treated. Not for nothing, but I hope you have a bottled water service as I would not want to drink that water. Iron is no big deal (just makes you constipated in high levels) but manganese is not good for you and, being near an old mine means lots of other potentially dangerous metals (cadmium, lead, etc). It’s like old apple orchards that are developed into housing communities - the ground water often has dangerous levels of arsenic in it

Anyway, sounds like manganese is your culprit. Maganese forms lots of different insoluble oxides and mixed hydroxide/oxide/carbonates are possible. So your water could be scaling out the Mn and the filter captures it. One thing you can try to do is put polyester pillow stuffing (poly fill) in your skimmer basket and try adding some polymeric clarifier to your water to see if you can get the particulates to agglomerate and fall out of solution into the polyfill. I would not use a flocculant as you have a plaster surface and no way to vacuum to waste.

 

[Swampwoman]

Maganese can in some cases be controlled with about doube the sequestrant needed for iron, or so I've read. Not sure if that works at your level.

One thing you can try for your staining is direct application of a HEDP based sequestrant, like Jacks Purple or Metal Magic, on the stains using a dishwasher wand...eg filling the tube with it. Let us know if that works if you try it. If it does, I have an idea, depending on the severity and path of your staining.

However, I should note that while maganese can look like iron, it can also be blacksh. Are you really sure you don't read for iron as well?

With metals, the best way to keep them in solution and avoid either tinting your water or staining is to avoid slamming f at all possible...eg keep your parameters according to TFP and you shouldn't need to ever slam. Also keep your ph on the lower side, eg 7.2-7.4 and see if that removes the tint.