Peace Lily leaves brown edges

My Peace Lilies' leaves have brown edges. The appearance is as though they had dried mud on the edges of the leaves.

I have had these Peace Lilies for years, started out as one plant that grew so much that I split the roots many times to make two plants. One smaller one even grew from a bit of root in a pot. So I don't think it is any kind of disease, as there are no recently introduced Peace Lilies, and the only other houseplants are an Aloe Vera and some hyacinths, the latter I only got a few days ago.

I just cleaned the leaves with plain water and cotton wool, the Peace Lily leaves didn't seem dusty, though the Aloe Vera had a lot of dust on its leaves. I had previously cleaned their leaves with plain water and cotton wool a couple of years ago, then let them dry outside for half an hour. They seemed to respond well to this. In my experience Peace Lilies do not like wet leaves. But a few months ago I put a tiny amount of washing up liquid in the water I used to clean the leaves, and they seemed to respond badly to that. I suppose it strips protective waxes off their leaves? I think I did think better of it and give them a final rinse with just plain water, but maybe this is why the leaves aren't as healthy looking as they have been?

I also found that about a year ago giving them Miracle Gro that I use in the garden seemed to have a negative effect on the Peace Lilies, it seemed to cause the tips of the leaves to turn brown. A couple of years ago somebody gave me some Bonsai Food, which contained a lot of trace elements, and I used it for the Peace Lilies, and they looked wonderful for that.

Just a few months ago the Peace Lily leaves were looking yellow, and I hadn't fed them for while, so I gave them a few drops of Baby Bio houseplant food in their water, and now the leaves are a healthy green colour again. A few days ago I turned them around, as they had been facing the window, and the side now facing looks very healthy and green apart from the brown bits on the sides of the leaves.

My Peace Lilies seem to like their leaves cleaned with plain water and cotton wool, and preferably dried either outside or with another piece of cotton wool, and they do need feeding but only with houseplant food like Baby Bio or that specialist Bonsai food, not Miracle Gro for garden plants. They are very forgiving about watering, and they have always managed fine by windows which don't get much light.

Also after cleaning the leaves a couple of days ago, I also cleaned the white "flower" in the same way, and now I am noticing it is turning brown around the edges, so maybe not a good idea.

Edit: I uploaded some photographs to show the brown areas on the Peace Lily leaves. I also noticed that some of the plants have roots coming out of the bottom of the pots, so probably need bigger pots or to be divided. The brown areas could be any number of things, maybe the Miracle Gro from ages ago, maybe forgetting to feed them (with Baby Bio) for a while until recently, maybe using a drop of washing up liquid in the water to clean their leaves. The leaves are looking greener since I gave them some Baby Bio a few weeks ago, before that some leaves were yellowing. And the "flower" definitely didn't like being cleaned with plain water and cotton wool that the leaves need.

 

I think the most likely cause of your leaf problem is too much direct sunlight on the leaves.
PLs love a semi shaded spot in summer and full light in the winter .
However, you do say that yours have always managed fine by windows that don’t get much light , so may be l am off the mark . PLs also love having their leaves regularly misted , as dry leaves can discolour. So , maybe this is a cause.
Baby Bio is brilliant feed , can’t go wrong with it !

 

My windows don't get much light. The Peace Lilies have never seemed to mind, but it wouldn't be enough light for a lot of houseplants.

I think I need to pay more attention to giving them regular Baby Bio, keeping their leaves cleaned of dust with plain water, and not cleaning the white "flower", which turned completely brown after giving it the same treatment as the leaves, and also sorting out re-potting and splitting them more often as they have roots coming out of the bottoms of their pots, and to avoid using anything but plain water to clean their leaves, and never give them Miracle Gro. I am not sure about the misting of leaves, you could be right but in my experience they seem to prefer their leaves not to remain wet. They are very forgiving plants, but I wasn't giving them enough attention recently.