When does a tank need C02?

[@ombomb]

I've got a planted 47.5 gallon community tank and some of my plants, (no idea what the name is but they are VERY fast growing with small 1"-2" leaves off a central stem) seem to be getting brown leaves on them.

I have a dual light hood, with two 36" flourescent bulbs and a Fluval 4 internal filter, although I am adding an Eheim external this weekend.

Could this be a lack of C02 in there?

I add plant food weekly at water changes and it's really on the one type of plant that has been affected. It's not a new problem, but it gorws so fast that the brownish bits can be pulled out and still leave plenty of plants.

I do want to add more plants but was hoping to try and solve this problem before hand.

 

[Cheese Specialist]

Maybe try testing your co2. If the plants are growing fast, you must be doing something right. Perhaps they just need pruning a bit.