oh boy ...confused on ash

I'm gonna work on transitioning my cat's diet to mostly if not all wet - but I am confused on ash content ...I think understand what it is & why it's important to consider but I don't understand what a 'safe' or 'healthy' level is

...most of the wet foods list 2.5 or less ...which I guess is not 'dry content' ...so I would expect wet food to have a lower ash content on the label, right?

He is a 2 yr old neuter male ...how low an ash content should I look for?  And, I read in an old post that I should look at magnesium too, not just ash but I don't see that on most labels...if any so far ...and what should that be?  TY!

Here is a good thread that discusses magnesium content as well as some citing some sources.
http://www.thecatsite.com/t/273313/fish-as-a-secondary-ingredient

Ash is the leftover mineral content after the food is burnt. It can be confusing as to how much is a good or safe amount. I don't think there is a set number. You also need to compare the ash amount on a dry matter basis if you are looking at both dry and wet foods.