have you by chance changed the filter recently?
i'm not really seeing anything glaringly wrong. stress-coat is fine, sort of expensive, i use it myself.... $26 a gallon at
www.bigalsonline.com
the things i would suggest are mostly along the lines of....
increasing water changes, at least a gallon a week, dechlorinate the water and try to keep the temperature close.(it should be cool to the touch)
vacuuming, this is another thing that sort of depends on the water changes, the more water changes the less vacuuming. every week would be ideal but possibly overkill.
you need another place for bacteria to grow, next time you change the filter dump the baggie out and maybe rinse it in tap water or dechlorinated water and put it back into the rear of the filter behind the new bag. you don't want it to impede water flow, but you want the water to go through it. this piece isnt for filtering it is strictly a place for bacteria to grow. (you can also use other kinds of floss, but i would suggest the "cut to fit stuff if you want to buy new.)after the new filter you put in gets nasty you can also rinse that in tank/dechlor water..... this will give you much more longevity per filter and save some money. don't worry about the charcoal, use it if it comes with it, but if you just rinse it shouldn't matter if the old stuff stays in. some people would reccomend discontinueing ti entirely, but if you get it free with the bags you might as well use it. only clean the filter or the pad in any given week, do not do both.......
test the water for the next several days for ammonia and nitrites, if the reading are 0 like 3 days in a row then the tank should be safe and you could replace some of the missing stock. i'm not sure i would add more than 1 every week or so, maybe a couple days less but not much. i would sort of start buying towards stronger fish too honestly, danios are good and small, i cycled one of my tanks with red eye tetras too........you could even go back to molly/swordtail types but they are very susceptable to the nitrites i think.
other than that, just keep up your water changes...... if anything seems funny do an extra water change or 2.....
i'm sort of wondering if you are being "too clean" by replacing the filter that often on a newer tank, possibly every time you change the filter you cause at least a small "cycle" spike until the bacteria recover. by adding the extra piece of filter material and only washing one piece at a time you should even be able to decrease the impact of mini-cycles somewhat.
sorry i can't be more helpful, just not picking up an anything as being glaringly wrong.