If your tank is still cycling then you have to do more water changes to keep you parameters in check. I did gravel vaccuming like either every other day or every two days when my tanks were cycling. Once my tanks cycled I do water changes of 25-30% monthly with a gravel vac. I was told that weekly water changes stress the fish out since I have been doing it monthly my fish are great and water parameters are perfect on all my tanks. See my sig....Good luck
In a heavally planted tank, {maybe} have you checked water parms. after 4 weeks. i'am not sure who told you that but 30% monthly is not enough..25-30% weekly is the norm.....