brown spots in tank/cloudy water

Question
Hi!  I'm gonna be honest and confess that I did no research before starting my aquarium.  I just bought a pre-packaged set-up kit, picked out fish I thought were pretty and hoped for the best.  I really didn't think there'd be that much to it.  Wow was I wrong!  The problem is I really love having a tank and I've been really trying to improve on my mistakes so far.  I have a 29 gallon tank, and since its set-up three months ago, I've done 30-50% water changes each and every weekend (including vacuuming the gravel with each water change).  I test regularly and my nitrite, nitrate and ammonia levels are good My ph, alkalinity and hardness are very high.  All the levels have pretty much been the same since set-up.  I've had one spike in nitrite and one in nitrate, but both resolved themselves within a day or so.  I don't add anything to my water to make it softer or lower any of the higher levels.  I want to try to find fish that will thrive naturally in the water that I have and not try to doctor it to change the levels.  My problems right now are these: 1) the water seems real dusty -- not cloudy, but like there's dust floating in it.  This hasn't gone away despite two water changes in the last 1-1/2 weeks, as well as a filter change.  2) There are brown spots on the decorations inside the tank.  Could this be some kind of brown algae?  I also haven't had much luck with the fish I've purchased.  I'm pretty sure I didn't cycle the tank properly and probably had fish in there that weren't hardy enough to cycle.  I had one gourami that lasted from the very beginning until today, and I think he died of dropsy.  As of now, there are 6 rasboras, 2 gold barb, and 6 tiger barbs.  I've tried mollies, platys, corycats, clown loaches and neon tetras.  All of those have died.  I don't want to give up on this because I really enjoy it and so do my children.  I just want my tank and fish to be healthy!  Can you help?  I'd appreciate any advice!

Answer
 I think a few simple things I am about to tell you are going to help you a lot.
First of all, the deaths may have a lot to do with your tiger barbs, they are aggressive fish, none of the others you have are, you have a bad match there.  I suggest getting rid of the tiger barbs!  Take them back to the store, put them in the paper whatever, just get rid of them. (not whatever, please please don't destroy them)  Those are my least favorite of all the fish I know so far, they look cute, but are anything but!  They can kill your fish in a second!
The water problem sounds like rock dust to me.  Did you clean your rocks really well?
Brown Algae, YULK!  I have been there.  You need yourself an algae eater, either a plecaustamus (sp?) or snails will do!
Hang in there, it is a fun hobby!  I have a 55g, 20g, 10g, 5g, and 2g.  Pretty much a tank in every room. :)  I enjoy them that much!

P.S. I don't stress on water at all, I don't ever check mine, and have no problems.