Gh/
KH should be the least of your concerns right now. Honestly unless you are pumping
co2 into your tank or have african cichlids/ discus it wont matter. Also, from my knowledge gourami's should be kept in at least 1-2 male female ratio. For a 30G I would only do one male and keep 2 females.
10 Gallon ; Marineland Penguin 150 ; Heater ; Sand Substrate ; 2 Zebra danios