"Food for thought" for anyone reading this thread.
Our vet recommended we not feed our boys that have had problems with calcium oxalate crystals any fish-based food or treats as apparently fish-based proteins tend to be high in magnesium.
And I posted a thread with charts in them if you want to look at the chart to see where your kitty is on the weight scale vs. where he/she should be: Ideal weight for cat
And I posted a thread with charts in them if you want to look at the chart to see where your kitty is on the weight scale vs. where he/she should be: Ideal weight for cat