Hi Coolie,
I converted a 30g tropical fish tank to a reef tank. It took some time and preparations however. My 30g tank has 10 coral pieces, liverock, live sand, a clownfish pair, bluefin wrasse and starry blenny.
I upgraded the light to (2) 65w power-compact bulbs in a
coralife fixture, added a hang-on-back skimmer from
Octopus and I have an
Eheim canister filter which I use for adding flow & filter media such as carbon. I also have a
Koralia 1 powerhead for additional flow.
After adding all this equipment, the conversion was quite expensive.
I noticed petco had a 29g BIOCUBE aquarium for $299.00 in the store (you can find it cheaper online too).
This tank has the "small" factor to help you adjusting into Saltwater keeping, but it also incorporates a lot of the filtering / lighting you will need anyway. I believe the only thing you will need to add to this tank is a skimmer.
An all-in-one nano reef such as the
BIOCUBE or
RED SEA MAX might be a good choice for you and you can use the 25g as a quarantine tank.....
If you're up for it, you could do a 55g (find a pre-drilled one if you can) and use the 25g as the sump system.....do your research though and take your time.
Everyone on this site has great experience and will help you with any questions you have.
Good luck to you....post some pics when you get going!