Hello !
Your post is good but needs a couple of comments.
Storing chemicals in a fridge is, generally, a bad idea as some times the mix broke and you get solid deposit in the bottom of the vessel. And morer often than not, they can't be brought back into solution... want to know how I learned it ?
The use of marbles is, at first, a good idea, but when they age, they tend to produce very small chis which could ruin the wonderful and perfect shot which will make you rich....
I've a better solution altogether which is better explained by an example :
Suppose you've a one gallon D76 stock batch freshly mixed. Suppose you need 150 CC of stock to process one film at 1+1 dilution because your tank need 300 CC chemistry to wet one 135/36 film. Buy a set of 150 cc glass bottles and 3 one liter glass bottles.
Measure 150cc D76 and put it in one 150 cc bottle. There is a certain amount of air above the chemistry. Fill this up to the brim with plain water, cap tightly and label as 150 CC stock D76 with the date mixed. Your bottle contains exactly 150 CC D76 and, of course, an unknown amount of water. When preparing the working solution for your film, put the entire content of the bottle into the measuring cylinder, add water to get up to the 300 CC mark and, voila ! You've got 300 CC D76 at 1+1 dilution. This way, your chemistry will last for a very long time provided your darkroom does not get ice cold in winter and oven hot in summer....
Generally, I put my developer in 1 liter bottles filled to the brim and the remaining from the gallon in the little 150cc bottles. (the 3.76 L D76 stock is split in 3 one liter bottles and the remaining of the 76 liter stock divided in 150 CC). When the set of small doses are finished, I split another liter into small 150CC bottles in the same way...
Hope this helps.