Carbon in a tank with plants ( adding fertilizer) ???

[Magnum Man]

Next thing… plants are good… lots of plants are better, but really are the fertilizers needed for some plants, good for your fish???
Probably some are less bothersome to the fish than others…
I have several fertilizers here, but like I said in my OP, I no longer use them… kicking the drugs was hard, and required changing out several plants, that wouldn’t thrive without the good stuff… but now all of my tanks, would be considered “heavily planted, albeit, most are one of a few terrestrial plants, but I’ve been really happy with this aquatic plant… this is with no fertilizer…

 

[Colin_T]

… my understanding of carbon, is that it’s like a sponge, so it’ll only hold so many “impurities” ( which could be fertilizer, or medications ) so it could be filled up with fertilizer, and not absorb anything else, and a second dose of fertilizer, then may be available to the plants, if it’s added regularly, if the carbon has already absorbed what it can hold, but that begs to question, why use carbon in a planted tank, in the 1st place, if you’re adding fertilizer???

That is correct. Once the carbon has adsorbed as much as it can, it will no longer remove anything from the water, which is why shops recommend swapping it out every 2-4 weeks. However, it's not needed in aquariums unless you have chemicals or heavy metals in the water, and if you do, then you should be filtering the water before adding it to the aquarium.

Fertilsers are not the best for fish, which is why you need to keep the levels low.