Don't a lot of brackish fish become tolerant of full "saltwater" salinity as they become adults?
I'm streaching my memory here, as it's been about 10 years since I tried a brackish aquarium.
Our First Tank - I've gotta give kudos to you for taking the comments graciously :thumbsup: - you'll find everyone has different opinions on how a tank should be set-up, and when it comes to corals we can go even more overboard on how to do it
Your tank is almost identicle to the first salt tank I started in college six years ago - a 30-gallon hexagon tank - I had a humu humu trigger, snowflake eel, and a few damsels; a 10-lb piece of live rock (that cost me a few nights at the bars

) and due to the bioload (because of my inexperience) it was an incredible algae-farm

. Not that I would ever recommend this to a beginner - just trying to show that we all have to start somewhere
Since you don't have live rock, you may not go through the classic saltwater "cycle" as there are many organisms that die in live rock, get eaten by bacteria, and then new organisms populate the inner crevaces and spaces in the rock (the stuff is like swiss cheese - very porus). This "death and rebirth" can take a few weeks to a month - hence the warnings about putting fish in a "polluted" environment.
Just keep an eye on your ammonia, nitrites and nitrates - you have a fairly good bio-load in there, so you may find that the above will gradually increase over time - ideally, enough bacteria will colonize the filter media, sand bed, and water itself to process any ammonia and nitrite. Ammonia and nitrite are non-existant in a cycled tank - however, nitrates will creap up over time as they are not processed by aerobic bacteria - there are ways to lower them, but at this point - just plan on keeping them down with water changes.
If you do test and have *any* ammonia, I suggest an immediate water change - due to the pH of saltwater, the ions in ammonia are 100X more toxic to fish than they are in freshwater - so the smallest amount may not kill your fish instantly, but will probably stress them out enough to have them croak in like a week
I'm sure you have a lot of questions - or you will. I know we're not supposed to mention other websites - but for those entering the hobby, I like to recommend wetwebmedia.com - the information there is very easy to read, and best of all it comes from experienced professionals - so you can "trust" it as much as you can trust any advice in this hobby :lol: I agree the "new to the hobby" forum can be very good to, as long as you know where the advice is coming from.
Ask all the questions you would like here though - locals are always willing to help - maybe with some live sand to get some detritus-eating creatures in your tank - or if you would like to see other systems - mine is always open for a tour
