How big is the discus and how big is your tank? Even though having only one discus isn't the best idea small discus are best kept in small tanks. For instance 3 2" discus would be best raised in a 20g tank till they are big and healthy enough to be comfortable in a larger tank. I have 6 in my 45 g and 3 are 2" and they hide a lot. I'm going to be moving them into there own 20g next week for 6-8 weeks to give them relaxed atmosphere.
if you keep them in a small tank (30 is small for discus) you won't even be able to keep young discus in ther long.
they need to be fed 4 X per day and small water changes either daily or everyother day...you need to remove the un eaten food and it's easier in a bare bottom tank and done frequently.
that said..discus will grow fairly quickly in the right environment. they need room to grow..in the right conditions 2" discus will get to 4" in a few shirt weeks.
they will not act correctly if kept in a small group and you may never see how a discus is suppose to act unless you get them in a group.
it takes them a bit of time to get comfortable..once they do..they will greet you every time you walk in the room...big males will 'display' to get your attention.
if you keep your discus in a 30 and they do not show good growth..you are probably slowing them by keeping them in a small tank.Ikept 3 in a 29 for 2 months qt..once moved to the large display tank 75 g with 25 g sump..they exploded with growth.