Japanese Peace Lily seems to be rotting

So I've had my peace lilies for about a year and I've cared for another in the past that survived 5 or so years. I've been told they should be watered from below to encourage growth and I've kept a watering diary so I didn't overdo it. I've been fertilising them roughly once a month and watering them once a week (now once a fortnight because it's a bit cooler and they don't dry out). There's a layer of stones at the bottom of there pots and everything was going well until one of them started wilting. I thought ok I'll give it a bumper of water and think about moving it to a bigger pot. But very quickly it started going yellow and then brown. I hadn't watered it again since it started to wilt and I assumed that I'd just given it a bit too much and when it dried it'd perk up again but it didn't. As some of the leaves started it lay on the dirt I tipped it all out of the pot to see what was going on underneath, fearing the roots were rooting. They did have a bit of white fuzz on some of them but the internet said root root made roots black and squidgy, which it wasn't. The bases of the stems though they were, and there was also a small colony of small maggots living in them. So I stripped the worst of the plant away, kept the healthiest together and hoped for the best. The best didn't happen and they all died.
It was unfortunate but I still had lily number two. But now the same thing seems to be happening to that one a few weeks later. I've taken out two small affected bits and left the healthy looking green bits behind, hoping that this time I've caught it early enough but I don't know what I've caught or what to do if the healthier parts still get sick. Has anyone experienced anything similar or have any experience with Japanese Peace Lilies and can tell me what I'm doing wrong?

 

It sound like root burning from fertilize , did you chance fertilize or changed the position to a sunny spot?

 

Just wondering if it might be vine weevil. Their grabs wreck the plants by destroying the roots. The grabs are fat and curled up with brown heads.

 

I was thinking vine weevil too. There is a solution you can buy for them but I can't remember what its called.

On a plant that's already died, you can do a post mortem. Gently shake off the soil from the dead plant to expose the root structure. Vine weevil grubs do a pretty good job of destroying the roots, so if there are few roots then vine weevil is a prime suspect, especially if you catch them red handed (the grubs in the soil).

If it is that, then you need to act fast and isolate affected plants if possible, because vine weevil is not limited to a particular species, it affects many plants.

look out for the parents, and squash them on sight. They look like this:

Vine weevil / Royal Horticultural Society

 

I haven't changed the solution or moved them before but this vine weevil sounds likely. I shall look into getting some pest control.