What is better, low ash or low magnesium?

When searching for good foods to feed a cat who has a history of struvite crystals, is it better to look for low ash or low magnesium? For example, I am currently feeding Eagle Pack Holistic Select. The dry has .099 magnesium and 4.3%ash. I was interested in switching to the Nutro dry (we are having a bit of a financial strain lately, since my Labrador was put on IVD his food alone is costing over 80.00 per month -- then I have a shep/akita/dobie mix and three cats to feed -- not to mention me and hubby!) The nutro dry adult is only .088% magnesium but the ash is 6.75%. So I am confused. The cats are also eating 50% canned food, which I rotate between Eagle Pack, Nutro and Natural balance and I will be trying Trader Joes soon as well. I noticed that the cans vary greatly when it comes to the ash as well, but they all say
.025% magnesium on the cans.

Ash is the mineral leval as a whole after the food is burned... today pretty much any premium is going to have a safe ash leval.... Magnesium I due watch since Kandie has crf and would prefer to protect Zoey as much as I can... If you have uti trouble I would say no more than .085 magnesium... I havent gotten the answer about .088 and uti issues... I would say .099 is right at the cut off of what I would fed..

which IVD is the lab on if I may ask??

I also watch the magnesium. I dont have my food label atm but I am sure mine is .08. Since Simba has been on this food he has not had another UTI.

Thanks for the replies. Maybe I will switch to the Nutro dry, as it is less expensive and also has a lower magnesium level than the Eagle Pack. I was nervous about swithcing though, when I saw the ash was higher. So confusing trying to do the right thing by these animals!!

My lab is on the IVD rabbit and potato. People told me that IVD is not a good food, but I have to say, he has been on it about a month now and it is like a miracle food. I tried soooo many other foods for his allergies, and this one worked immediately. Unfortunately, he eats 40 lbs of dry per month (he is very active) which costs 80.00 and I also give him the canned IVD in his kong and sometimes mixed in his meals, but I had to cut him back because the cans are 2.00 each. But I won't stop feeding him this as I dealt with allergies for an entire year and this is the only thing that works.

IVD is a good food ... ahh you have a big allergie problem... so sorry for you pup...

Don't feel sorry for him -- he absolutely LOVES his new food! And, no more ear infection, staph, hot spots or runny poos.

Instead, feel sorry for my pocket book

But actually, now that i won't have to bring him in for a vet visit, antibiotics, steroids and ear cream every few weeks -- things are looking up!!

As for the cats, I think I will stay with Eagle Pack, for their dry food. (I rotate the cans) Mew was on Eagle Pack since we adopted her last March. She did not get the crystals until we switched to one bag of Chicken Soup for the Cat...blah, blah, blah.. and I only switched because my Eagle Pack order was not in on time and we were going away for four days.
So, I am afraid to try the Nutro now, even if it is lower magnesium and cheaper, since the ash is higher.
We were originally doing mainly dry, with canned as an extra.
After mew was diagnosed with crystals in the beginning of December I tried for all canned, but soon found we couldn't afford it, and am now currently doing one meal canned and one meal dry. Seems to be working out well so far. If my finanaces ever change in the future I will go to all canned, with the dry just as a treat.

I know someone will say something... but which eagle pack?? Kandie was on the holistic and my vet went nuts... pm me and I will tell you why...

the ash issue talk with your vet ... mine made it crystal clear