Can Sequestrant Lower FC?

[xtrsports]

Hey... before getting to my question, just wanted to say thanks, I post very infrequently because the experts contributing to this site answers nearly all my questions.

Background.
I've got well water with high metals and a small leak in the pool. There is an automatic pool leveler that adds water automatically. After about two weeks I the pool turns clear but with a green tint. To cure the tint I've been adding a product called pool magnet plus from Bioguard which seems to work well. This time I combined two quarts of the pool magnet with 2 pounds of powered sequestrant. (probably not good but....)
pool size is @ 40k gallons, gunnite,
chlorine generator

On to my question...
Prior to adding the chemicals last night I had FC of 3.5, then I added the two quarts of pool magnet plus and 2lb of sequestrant (as per the directions for my size pool). I left the pool over night with pump off (therefore chlorine generator not running). In the morning I had 0 FC. Stabilizer at 80. Pool crystal clear and blue with no algae but just curious to know if there is any correlation with adding the chemicals. The label on the sequestrant suggests not shocking the pool so I'm waiting a week and holding my breath that I don't get an algae bloom. Note that I also tested the water coming off the chlorine generator directly and it isn't showing any difference in the FC levels, salt at 3k ppm. Perhaps the chemicals are giving me some false readings?

Let me know if you need any other test data and I'll update with exact values but total alkalinity and PH seem to be good.
Thanks again

 

[chem geek]

The BioGuard Pool Magnet Plus is HEDP so only slowly breaks down from chlorine but you didn't specify what the powdered sequestrant was. If it was something like EDTA, then that consumes chlorine more quickly so may be what happened. What exactly is the powdered sequestrant -- the brand name and, if listed, the ingredients? This is one of the reasons we recommend using only HEDP-based sequestrant.

 

[xtrsports]

United Chemical, Pool Stain Treat, Sequestrant & Chelator. It doesn't list the ingredients but does say that it contains oxalic acid on the warning label. On a side note, it has done a wonderful job in eliminating the stains on the bottom of the pool.

 

[xtrsports]

also... I didn't see HEDP or EDTA listed in the helpful terms section so don't really know the difference between the two. I'll do some additional searching as I'm sure you or others have mentioned it in prior posts.

 

[chem geek]

In the Metals in the Water and Metal Stains Pool School article:

Sequestrants based on HEDP, phosphonic acid, or phosphonic acid derivatives are the most effective. ProTeam's Metal Magic and Jack's Magic The Pink Stuff (regular), The Blue Stuff (fresh plaster), and The Purple Stuff (salt) are some of the top sequestrants. You can also find many other brands with similar active ingredients, some of which are noticeably less expensive.

As for United Chemical Pool Stain Treat, the MSDS indicates oxalic acid and that is similar to the ascorbic acid we recommend for removing metal stains (though oxalic acid can sometimes do better with copper stains while ascorbic acid is fine for iron stains). Oxalic acid, like ascorbic acid, is a reducing agent so will consume chlorine so that explains why the chlorine dropped.