Chem Geek's "Yel/Mstrd Min" field

[DonW]

I nuked the pool this past weekend according to the Chlorine/CYA Chart by Chem Geek for a mustard algae problem that we have been having. Our CYA is 80 so I shocked and held it for 24 hours at 46 ppm. Nine cases of 96 oz 6% bleach later, (36 jugs!) I think that I've got the upper hand. However I don't understand a field in the chart. It is the "Yel/Mstrd Min" field. Is this for folks like me who have had a yellow mustard algae issue? Should I not let the chlorine fall below this level? If it is, how can I get a true ph reading then?

 

[polyvue]

[What] is the "Yel/Mstrd Min" field. Is this for folks like me who have had a yellow mustard algae issue? Should I not let the chlorine fall below this level? If it is, how can I get a true ph reading then?

As I read it, yes it's the minimum chlorine level for pools being shocked for mustard algae. You want to target the maximum level and not let it fall below the minimum.

I don't know of a method to obtain a true pH reading with chlorine levels higher than 10 or 15. Usually, you want to take a base reading for pH before shocking. My understanding is that liquid chlorine does contribute to pH rise, but I don't have any estimate handy. Perhaps someone else here knows this.

NOTE: A reasonable approximation to the above table is the following:

.... "Yel/Mstrd Min" is 15% of the CYA level

Source: Excerpt from Chlorine/CYA Chart by Chemgeek

 

[chem geek]

The "Yel/Mstrd Min" column is the (presumed) minimum chlorine level for preventing yellow/mustard algae growth in pools that already have such algae not completely killed, perhaps still hiding in light niches or other areas. If you truly completely get rid of the algae by shocking at the "Yel/Mstd Shock" level for at least 2, if not 3 days, and put in poles, brushes and other items used to clean the pool and got behind light niches and under ladders, then you can just use normal minimum chlorine levels after the shocking is complete.