I posted in the ferts and water parameters sub to get advice on whether I can get away with dosing an all-in-one fert without harming my fish and inverts and after some discussion I've decided to give it a go. I have some pretty ratty looking java fern (pic below) that I've hidden in the back. I'm hoping that changing the fert routine will help them bounce back, although it will probably take a really long time.
Currently I am dosing a product that the LFS foisted on me when I first started fishkeeping. It only has micros and K, but no N and P. As I understand it N and P are produced by fish waste, so in a very low energy setup additional N and P might be unnecessary. Mine is a low energy setup, with super low light (I'm using the dimmest setting on a Chihiros A series light) but I feel like I should have enough plants in there that will benefit from additional N and P without harming the livestock. So I'll probably head out tomorrow to get a bottle of Tropica specialised fertiliser and start giving my tank one pump a week after my next weekly water change, and monitor from there.
Shrimp are still hiding, I think it's probably my fault, my last couple of water changes were especially stressful for them since I moved around nearly all the plants and hardscape trying to clean out all the detritus underneath. They probably hate me, so I'll stop disturbing things when I do my water changes from now on. I will probably also get the API GH and KH tests tomorrow.
There are still a couple of crevices between the rocks like in the picture above where I can stuff more plants. I'm thinking of getting a couple of bucephalandra green wavy rhizomes to fill these little places out. Also not sure if you can see but in the middle there is a shrimp sitting on top of a Glasgarten dinner pad. That is where I've decided to put shrimp food since it's pretty much the only place where my corydoras can't reach. Corydoras may be shrimp safe for the most part, but they sure as hell aren't shrimp food safe.
Finally this is just a picture of the tank as it looks like today. Had to increase the light intensity briefly so that I could take this picture so that my reflection won't be so obvious. Nothing is dead as far as I can tell so that's good.