Help Now Please

[Miss Dib Dabs]

I'm worried why the fish that died was skinny, did she eat well, as i'm thinking she might off had internal parasites, did she die in the tank, and can you remember what it looked like when she went to the toilet, check on the other as well for going to the toilet, is it long white and stringy.

One of my platties appears to have started doing white poop, although not long and stringy. Just lil bits and they don't sink like you would normally expect. The nitrate was ever so slightly up this morning and I've done a 20% water change today.
Hugs,
P.
Edit:Having added two new fish to the tank tank today (a harlequinn and a tetra, had a single harlequinn b4 so now have two and have 4 of the tetras with the two red platties). I'm wondering if that upset it? She and the other plattie are looking very well and are very active otherwise. Sorry to add this on here. Just seemed better then putting a new post up.

 

[twinsmom]

Geez as if I don't have enough problems, my pleco just swallowed a ghost shrimp. I had 10 a few days ago, one died yesterday which I posted the pic of, and now I have 5 left. My filtered tap water nitrate level is 0

 

[WILDER]

That's brillant that you have a tap reading of nitrate in 0, it's mean that your tanks isn't coping with the load.
White stringy poo just try a shelled pea for a few days first to see if it's constipation, is the anus red and inflamed, can you see anything prutruding from it.