Plants Nutrient Deficiency

Hello, I need some help from you guys about my plants (I'm a newbie btw, so hello to you ). Recently, my plant's old leaves keep turning into yellow colour, then turn into some kind of dirt brown colour. I think they are dying. The newly grown leaves don't seem to grow up anymore. I don't know which nutrient(s) my plants need. I've add some "liquid fertilizer" into my tank for 2 weeks now and the plants are still dying. Here are the conditions of my plants right now.
P/s: I'm 99% sure the problem is not about the amount of light.
Thank you.

 

While you wait for some responses this thread may be useful
Deficiency List for Plants

 

Wow, thank you so much

 

Please excuse my manners I forgot to say Welcome to Fishlore, hope you enjoy the forum

 

hey there! what kind of liquid fert are you using? a lot of liquid fertilizers don't have all the nutrients a plant needs.

I would highly recommend taking that plant out of the pot and rock wool!! always do this after you buy a new potted plant. carefully scrape off the rock wool with tweezers and then trim the roots a bit to encourage new root growth. that's an anubias plant, so you can tie or superglue it onto a rock or some driftwood, even a tank ornament.

you can bury the roots in your substrate, but leave it looking how it looks now: don't bury the thick base where all the stems grow from.

if you want to keep it in a pot, just buy a tiny terra cotta planter and fill it with some substrate. then plant it as said above.

 

Thanks you ).
As for your question, i'm from Vietnam so i'm just using some Nuphar liquid fertz. It's a Vietnamese brand. It provides (at least the bottle said so) N,K, Mg,... and some type of acid, hormones,...
I've just done what you told me to do. I've put it in a tiny recycle polypropylene cup (I poked some holes on the cup too) and filled it with some substrate.
But what nutrients do you think my plant needs ?

 

i'm not very good with identifying nutrient deficiencies, unfortunately. that guide might help but it's a bit overwhelming. I use an all-in-one eI fertilizer, but i'm not sure what's available in vietnam.

it looks like your fertilizer has some macro nutrients, but not micro nutrients, if that helps.