Question about Milwaukee PH pen

[Grumblez]

My Milwaukee PH55 pro test pen came with a rubber and hard cap. The rubber doesn't fit on underneath the hard plastic cap. Is there a specific difference in purpose between the two caps or one I should be leaving on? I've been using the soft rubber on because it says to store it with a tiny bit off the storage soloution and it seems like the hard plastic one would require quite a bit.

 

[Grumblez]

Bump

 

[Randy Holmes-Farley]

Either one is fine.

Storing in diluted seawater is also fine. Say, 20% tank water and 80% RO/DI.

The main things to not store it in are pure RO/DI (draws salts out of the bulb) or 20+ ppt artificial seawater (that can precipitate calcium carbonate onto the bulb).