NO3,Hardness,Alkilinity: off charts, HELP?

[always learning]

I finally got the Quick Dip test strips and tested some stuff, here're the results:

NO3 200-250
NO2 0
Total Hardness 300+ (very high)
Total Alk. 30
pH 6

(ammonia not included)

I was under the impression that my aquarium would at worst be a little off, clearly I was wrong:

pH I can take care of myself but I need help with the other stuff

Point:
How do you raise the Alkalinity?
How do you lower NO3 (will just plants work?)
How do you lower Total Hardness?

Livestock are:
1 Tiger Oscar
2 Columbian Sharks
2 Rainbow Sharks
2 chiclids (Jewels maybe? they've got red bellys and reflective spots)
3 plecos (varying sizes)

30gal

 

[Blinky]

Looks like you've got a bit of work ahead, but it's fixable, don't worry.
It looks to me like your tank has 'Old Tank Syndrome', meaning that because it's overstocked and possibly water changes are not done as often as they should be (possibly the tank has been 'topped up' but water doesn't actually get taken out and replaced), the levels of wastes and solids have built up over time, and the pH has lowered quite a bit.
DON'T do a huge water change to try to right things all at once. This will shock the fish - they're used to their environment, so you want to adjust things gradually until the levels are where they should be.
I'd start with a 10% water change. Do this daily, and maybe after the first few days start changing 20% per day, then 30% after a few more days. Keep testing the water as you go along. Keep a record of all the levels; you want things to slowly get back to normal. You don't need to do anything but change water for now - I wouldn't add chemicals to change the pH, or add plants, or make any other significant changes.
Once your NO3 is ~20ppm or less, and your pH has stabilized, start a routine of regular (weekly is what most of us tend to do) 30 - 50% water changes - keep an eye on your NO3 levels as a guide; when it's over 20ppm, it's time to change some water
On another note, your tank is overstocked. All of the fish you have are destined to get very large (some over a foot in length), and a 30g just isn't large enough, even for one of them. Unless you're planning to get a much larger (several hundred gallons) tank, you're going to need to return some or all of them to the store.