Battling ascorbic acid...

[poopsmith]

So I've been battling metal stains with ascorbic acid, I've probably attempted it at least 3 times and the stains have returned each time. It's getting frustrating and expensive. Most recently I added ascorbic acid on Monday evening, circulated for an hour or so, stain was basically gone, I added 3 bottles of jack's blue stuff, then turned on the filter. Tuesday morning the stain was completely gone. Tuesday evening, I checked levels an I was at:

FC 0
PH 6.8
CYA ~35
TA 70

I decided to proceed slowly and using the pool calculator for my 30000 gallon vinyl pool, I figured I'd bring ph up with some baking soda, I figured I'd shoot low and try to bring it up to 7.0, so I added 48 oz of baking soda by volume dumping it in front of returns. I also figured I'd aim low on the FC, so I shot for FC 2, which was like 124 oz. We apparently had a pretty good storm overnight, when I woke up this morning it looked like the stain had returned on the liner. I checked FC and PH and as expected FC was at 0 and PH was somewhere between 6.8 and 7.0...

Any advice before I run off and get more ascorbic acid and sequestering agent? Like I said I've done this a few times, the first time I think I shocked too soon, the second time everything seemed ok and the stain was gone for like a month, then it returned and offhand I can't think of a reason, my PH was consistent around 7.2 the whole time, and I was holding my FC in my CYA range, this time I'm just plain baffled...

 

[JasonLion]

Welcome to TFP!

The most likely problem is not using enough sequestrant. The amount of sequestrant you need to use varies from pool to pool. At the first sign that the stains are returning you should be adding more sequestrant and that should make the stains go away again.

The size of the initial does of sequestrant and how frequently you need to add additional sequestrant both vary from pool to pool. In a few cases the amounts required can be substantial. The more metal there is in your water the more sequestrant you need. The simplest way to figure out how much you need is to watch the pool and add more at the first sign of stains. After a while like that you start to get a feel for how frequently you need to add more.

 

[poopsmith]

Just to clarify, you're suggesting only adding more sequestering agent or more ascorbic acid and more sequestering agent? Is sequestering agent enough to lift the metal that's fallen back to the pool surface?

Another problem is the choices of sequestering agents, my local pool store sells Pool Baron's Metal-X Plus, another has Jack's Blue, and Lowes has Dupont's Metal Remover... I'm unsure of which to go with, Jack's is somewhat more expensive, at like $23 a qt, the Metal-X and Dupont's are like $14 a qt... If I recall Jack's directions says initial dose is 1 qt per 10k gallons (which is what I did on monday), I think Dupont's is the same, the Pool Baron's says 16oz per 10k gallons, so it's a bit confusing...

 

[JasonLion]

If the stains have only been there for a day or two, sequestrant alone, or perhaps with a slight reduction in PH, will almost always remove them. Once the stains have been around for a while you need to use more ascorbic acid. This is what I mean about keeping an eye out, if you can catch the stains when they are brand new they are much simpler to remove.

Sequestrants based on HEDP, phosphonic acid, or phosphonic acid derivatives are the most effective. My two favorite brands are Jack's Magic The <pick a color> Stuff and ProTeam Metal Magic, but they are often the most expensive. By shopping around you can often find something less expensive that still work well. Not all of them are nearly as effective. Once you have a routine with one of the better brands, so you have some idea of what to expect, you can try out the less expensive versions and see how they compare.

You can often save a good deal of money by ordering over the Internet. I have seen Jack's Magic The Blue Stuff for $17/bottle in several places. Often there is shipping on top of that, but in most cases the shipping isn't too bad if you order several bottles at once.

 

[poopsmith]

Following up, it's been a couple days over 2 weeks since my last try at ascorbic acid...

Late last weekend the pool turned very cloudy. My conditions sounded a lot like the last post in this thread by gtm: slightly-cloudy-water-t10942.html

I'd say i had about a foot of visibility, I gave it some POP but after about 5 days I saw no gradual improvement.... During that time I measured 0 CC and kept my FC at slightly above my minimum suggested FC level. I went ahead and poured in some floc, shut the pump off overnight, and that helped it settle to the bottom by the next day. There was a ton of whatever the Crud was on the bottom, so I vacuumed it out, refilled, and did the same process the next day. So two days of vacuuming and filling, so I added more sequesterant. Turning the pump on still seemed to stir up some more and cloud the water somewhat, this time I can see in the shallow end, but not the main drain in the deep end.

Today I got some different test results:

FC 2
CC 0.5
PH 6.8
CYA 20
TA 80

I assume the drop in PH and CYA was due to the massive refill I had to do following flocing and vacuuming...
I added 83 ounces of CYA to bring it up to 40.
I added 128 ounces of borax to bring ph closer to 7.2, it's all I had on hand and it leaves me about another box to go (should I go ahead and try to get ph up to 7.4 or should I keep it at 7.2 following ascorbic acid?)
I added 52 ounces of 65% cal-hypo, which I had on hand, I didn't have enough bleach to get up to my shock level at 11 with a 20 CYA, I'll test the chlorine tonight and in the morning to check for a drop.

Does this all seem reasonable and does anyone want to offer any criticism or pats on the back?

 

[JasonLion]

You want to raise the PH and FC levels slowly after an AA treatment. Raising either one can cause the stains to return, so you want to move slowly enough that you can add more sequestrant if your have to.

Other than that, what you are doing sounds fine.