Hi Cinder...
I agree that your tank is probably at maximum. Could be the reason your nitrates are high. Frequent w/c's like you are doing will keep them in check tho.
As far as the gourami's...I have found it best to have at least 2-3 females for ONE male. I no longer keep gourami's...but in the past..the aggression eased up this way. HTH.
