Hi lashalove, sounds to me like you have done your research, good for you
I use mostly tap water that I let sit in a bucket overnight w/ an airtube to help remove chlorine, also use Stress Coat. Our tap water is VERY hard so our pH is about 8.2. I sometimes use R/O water when doing water changes just to soften it up a bit.
Only because you have tetras, try to keep it as close to 7. or lower as you can. Without using chemicals, you can add peat moss to the filter, that will help. Also adding drift wood will help.
I seem to be having a problem with brown algea, I've read the advice @ about.com and have been thinking about getting an otto or 2. The algea is so bad that I have to clean the tank about every 4 days (i.e. take out all the plastic plants & ornaments scrub good w/ very hot water, scrub glass, vacuum gravel.... remove about 15% water. I have an aquaclear 200 filter (3 stage) which I rinse in the removed water, and replace media as stated in the directions)
What wattage of lighting do you have? To much light & to many nutrients in the water will cause BA. Cleaning ALL the ornaments, glass & vacuuming. and doing a water change at the same time is the reason for the Nitrite spikes, your cleaning to much of the bio out. Scrub and rinse all decor as you would your filter medium, in old tank water. Bio grows on everything, not just in the filter.
Water temp is 75.
For the tetras sake, bringing it up to 78-79 would be appreciated
My Nitrate and Nitrite levels get pretty high and would go into the danger zone if waited more than 4 days to do a water change/cleaning.
As I said, don't clean and water change at the same time. Clean filters, etc only when needed and Water changes are just water changes, not cleaning. I would recommend more of a 30% a week. I actually do a 50% weekly on most of my tanks.
My mom said I might be feeding them too much... I give them a small pinch of flakes 3 times a day. Every 3 days or so I replace one of the meals with bloodworms. And the pleco gets a algea wafer after cleanings.
Watch them, and see just how much hits the bottom, and adjust to that. The Cories will help with the clean up, but not all.
BTW, most people think Cories are scavengers, they aren't, they like live foods and shrimp pellets
Now to my questions:
Is there anything I can do so I don't have to clean the tank so often?
Get your water stable first, then worry about the aesthetics
Do I have too many fish, can I get more? I'd ideally like to get 2 more bloodfins, 1 or 2 more coris, 2 more harlequins and maybe and otto or 2 for the brown algea? (getting rid of the guppies is an option)
you could add more, but get your Nitrite under control first, then add slow.
BTW, that common plec will get HUGE
Am I doing anything else wrong?
NO, as long as you are willing to ask questions & learn..... your doing things right 