MetalMagic impact to CH - cannot find anything on the forum

[MasterTinkerer]

I posted a thread a week ago about iron and copper levels in my pool and slight staining on my liner (Metal (Iron Copper) Levels - what to do)

Since then, I've spent the last week reading older threads here regarding metals and staining. Seems like there are a lot of folks dealing with stains and no good solution really... but all of my reading leads me to a question that I cannot find an answer for...

What about CH?

The description of MM on the back of the bottle says it will "quickly remove iron, copper, manganese and high calcium hardness from pool water"

So... do I need to add calcium chloride after I add the MM?

Given that it is a sequestrant, am I not just defeating the purpose of adding it?

Hard to believe that there is not a better solution out there...

 

[JoyfulNoise]

The amount of calcium hardness removed from the water will be trivial compared to the total amount. You would have to add dozens of gallons of the stuff to have any significant impact on CH.

It's greatest affinity is for divalent metal cations (Ca, Mg, Fe and Cu). Typical iron and copper levels that most people treat are in the 1-3ppm range. CH is measured in hundreds of ppm.

 

[MasterTinkerer]

The amount of calcium hardness removed from the water will be trivial compared to the total amount. You would have to add dozens of gallons of the stuff to have any significant impact on CH.

It's greatest affinity is for divalent metal cations (Ca, Mg, Fe and Cu). Typical iron and copper levels that most people treat are in the 1-3ppm range. CH is measured in hundreds of ppm.

Thanks Matt! Somewhere in one of the many posts that I read, I swear that I saw something about the initial MM treatment lowering CH levels by hundreds of ppms... that is what had me so confused. I couldn't understand why that was not mentioned anywhere... guess that I have the answer now... it wasn't mentioned because it is incorrect.

 

[JoyfulNoise]

Thanks Matt! Somewhere in one of the many posts that I read, I swear that I saw something about the initial MM treatment lowering CH levels by hundreds of ppms... that is what had me so confused. I couldn't understand why that was not mentioned anywhere... guess that I have the answer now... it wasn't mentioned because it is incorrect.

I think the problem most people run into with any kind of sequestrant is that it interferes with the CH test. Remember that the CH test is just a chelating titration test - you are adding drops of EDTA (R-0012) that suck calcium ions away from the Eriochrome Black indicator dye because EDTA has a greater ligand strength with calcium than EB does. If you add a powerful sequestering agent to your pool, like Jacks or MM, then the EDTA might not be able to pull all the calcium away from it and the CH will appear A LOT LOWER than it actually is. The Taylor CH test assumes that there are no sequestering agents in the water sample.

The only way to do a CH test (or any metal test) when sequestering agents are present is to do an acid digestion step first using a powerful acid/oxidizer like nitric acid. That will destroy the sequestrant and then put the metal ions back into solution. Then one can use a standard test for metals (CH, iron, etc). Acid digestion tests are often more expensive than basic metal test kits.

 

[MasterTinkerer]

Results of adding MM and a few questions... your input is appreciated!

Results
OK - added the two quarts of MM per the instructions on Wednesday night and let the pump run. Thursday when I got home from work in the afternoon, the stains were gone! Hooray!!

Added a jug of bleach Thursday also (121 oz at 8.25%). We've been getting a bunch of extra water - rain from the hurricane.

Did a full batch of tests Friday evening. Here are the results:
FC: 3
CC: 0
CYA: 30
PH: 7.4
TA: 60
CH: 125 (no impact from MM addition - same as test on June 10th)
Borates: ~40
Salt: ~2000 (I added salt for the improved feel when I opened)
CSI (per pool math): -0.86

Questions:

1. I had previously raised the PH to ~7.8 after I read several posts suggesting that it was better slightly high - more stable (I believe). Now that I know that I have staining issues, I guess I need to keep the PH lower. Input?
2. I've read that the target CYA should be 30-50. I find that I'm adding a jug of bleach every other day. Does this sound right? Should I consider raising the CYA or does the FC consumption seem appropriate?
3. Now the CSI is highly negative... should I be concerned? I had planned to add Calcium Chloride to raise my CH... how does the CH relate to potential metal staining in the future?
4. Speaking of adding calcium chloride - I got a bag of ice melt from Lowe's - SafeStep 7300. Safe Step® 7300 Calcium Chloride | SafeStep. Any experience with this product? If I'm understanding the Product Data sheet properly, it is a minimum of 73% Calcium Chloride. Not sure if I should dump it in the pool...
5. Anything else that I should know in the endless cycle of PDCA otherwise known as pool chemistry? Especially relative to the fact that I know I have potential to have iron stains?

 

[basod]

You have a vinyl pool there is no reason to increase your CH.
if your pool is in full sun all day running your CYA closer to 50 will help with the FC demand but all pools are different
a jug of bleach every other day is fairly normal.

Usually running pH on the lower end 7.2-4 will yield less metal staining but the MM you added will need to be added again as it is broken down.