We need water stats to really help you out. What is temp, ph, gh, kh, nitrate, nitrite and ammoniun levels. Due to this tank running as a planted tank for 3 to 4 weeks you are still going thru tank settleing in. As a result things will get out of wack and spike and you need to do bigger and more water changes for the next week or so till things settle down with water parameters.
I would get a bristlenose for this tank also to help with algae control.