Chem Geek or Mbar - are you there? Iron test question.

[labdi01]

I have a quick silly question, that I couldn't find the answer to when searching the Forum.

Does sequestered iron (which if I understood Chem Geek correctly from another post, are iron ions) show up on a pool-store iron test?

I'm Dianna (labdi01) - the one with the homemade quilt-batting filter ("New Pool Owner Manually Removing Iron"), that we ran for 72 hours after shocking turned my pool opaque brown and it cleared it up beautifully.

I went to pool store today to have water tested and they told me I have 5 ppm of iron, when my pool is perfectly clear, numbers mostly where they should be.

CL - 3
FC - 3
pH - 7.2
Alk - 130
CA - 50 (told me I had to bring it up w/ 10 lbs of Balance 300 - I ignored him)
CYA - 100 (claims that's fine - I understood this to be a problem from the Forum)
Iron - 5

I came home after this visit and shocked w/ 2 lbs of HTH Super Shock and Swim, with the intent of knocking any sequestered ions out in the open to be filtered, and my pool remains clear (it's only been about 10 mins after shock).

Could either or both of you shed some light on the iron result?

[aylad]

I'll leave the iron comments to the experts, but I will say that a FC of 3 with a CYA of 100 is not going to leave your pool clear for very long. You really need to either drain/refill half your water to get it down, or get your chlorine up to the 8-10 range, otherwise you're going to have problems keeping the algae away.

Janet

[labdi01]

I forgot to mention what my iron levels had been...

When first opened and shocked (water turned opaque brown) iron was 3
After 6 quarts of sequestrant and several days (water was clear/green) iron was 0.5
After adding 6 gals of bleach (water was opaque brown again) we didn't test
After filtering to clear iron was 0
Attempted an ascorbic acid treatment, didn't add anything but acid and 1/2" water (with batting filter in pool and prefilter on hose) for the last 48 hours
Now it's 5

???

[labdi01]

Thanks for your reply Janet.

After I got those numbers, I shocked with 2 lbs of HTH Super Shock and Swim, so hopefully, that brings my chlorine up beyond 8/10, no?.

[aylad]

Oh, sorry, I missed that the first time I read your post. That probably did bring it up beyond 8, but you're going to need to keep it there, at least 8, for as long as your CYa is that high. Not sure what the chlorine source of Super shock and Swim is, but if it's dichlor you need to stop using it because it raises CYA even further. You're probably okay for awhile if it's cal-hypo, but when your calcium numbers start getting past 200 or so you'll need to switch to bleach or liquid chlorine.

Janet

[labdi01]

Super Shock and Swim is Cal Hypo.

Actually, they said my calcium was low - so that might actually prove beneficial!

[labdi01]

My Taylor 2006 kit just arrived 10 mins ago! No more pool store!

So, the store told me this am that my CYA was 100. I did the Taylor test for CYA. The first time I did it - my CYA registered 40. I had some water left and tried it again. I didn't have enough to make the dot disappear, but I could still see the dot when I ran out of treated water - and that stopped at 60. I think the kid at the store did it wrong!

So, I did my chlorine - this is where I might be in trouble. My FC was 60 and my CC is 4.5 (I shocked at 10am with 2# cal hypo to scare out any metals).

Do I have a new problem on my hands because of the CC?

[Watermom]

Try those chlorine test again. I can't imagine that your FC is actually 60 and CC is 4.5.

Also, is this a vinyl pool? (I can't remember from your other thread.) If so, you don't need calcium.

[labdi01]

I goofed Watermom! I misread the instructions and multiplied by 3 not 0.5 (don't ask). So my CL is 15 and CC is 4.5. I read horror stories about getting this balanced (someone used over 100 gallons of bleach.

I do have a vinyl lined pool (AG 24')

I did the rest of the testing, too.

FC - 15
CC - 4.5
pH - 7.2
TA - 60
CA - 50
CYA - 50

My only concern about my numbers from the Taylor test is there were 2 incidents where the color they described was not the color I got - but adding more reagent didn't make a diff. Example - in the TA test, my color was supposed to change from green to red. I got more of a magenta. The calcium test said solution should turn blue. I had more of a indigo/purple.

With a CYA of 50 - I removed the CYA sock from the pool (this am pool store told me my CYA was 100 - but I did Taylor twice and got 40 and 50 respectively).

[chem geek]

Does sequestered iron (which if I understood Chem Geek correctly from another post, are iron ions) show up on a pool-store iron test?

I came home after this visit and shocked w/ 2 lbs of HTH Super Shock and Swim, with the intent of knocking any sequestered ions out in the open to be filtered, and my pool remains clear (it's only been about 10 mins after shock).

Could either or both of you shed some light on the iron result?

I had that same question and asked Taylor Technologies about it a while back and basically the iron test that they use and probably ones that others use test all iron that is present including that which is sequestered since the sequestering agents bind the metal ions somewhat loosely in an equilibrium so that as the free metal ions get used up in the test more are released from the sequestering agent. This is similar to how the FC tests all chlorine including that bound by CYA.

So that would explain why you still measure iron in your pool, yet it is clear. It also explains why you are not able to precipitate it because the concentration that is unbound is fairly low so would take a heck of a high pH to be able to form precipitate (i.e. the metal sequestrant is doing its job well).

Unfortunately, that means there is no easy way for you to tell your "free" metal ion level other than seeing that the water is clear and that you aren't getting any staining. The 5 ppm of iron the pool store is measuring is mostly bound to your metal sequestrant -- you must have used quite a bit of it to sequester that much iron.

The better sequestering agents are slower to get oxidized by chlorine so it isn't easy to break them down to release the iron, but that's the point of a good metal sequestrant anyway. You don't want it to break down easily because if it did then you'd have to add more much more frequently and it would also increase your daily chlorine demand.

Richard