I would reccomend having a ph test first test your tapwater rested for 24 hours then compear it to the ph inyour tank thelower ph is the slower bacteria reproduce so if ph is at 6 bacteria go into a dormant stage or may even die if your danios are still alive consider yourself lucky that they acclimated but also check your tap water ammonia nitrite and nitrate just in case because it could mess up your results if ammonia is dark green or turns into purpilish blue it is way off the chart do a 100% water change and you should still have ammonia in the tank i did this and i still had 2 ppm ammonia if ammonia keeps trying to spike just lower your ammonia ur goal is to maintain lower than 5ppm for api testkits lower or at 4 ppm just dont gravel vac unless you have fish and if you dont have fish put your heater to 80-81 degrees Farhenheit good luck and consider your self lucky because when i found all this out i had wasted 4 months of my time with no ammonia down no nitrites or nitrates the reason i say it's important to keep your ammonia down is because if level rise above5ppm it can inhibit bacteria growth and your cycle will stall or they just stop reproducing due to the bacterias bio feedback mechanisim just have patience even though its hard
ps once you see nitrites keep it low too dont let it get to high and nitrates the final result can be kept under 20 ppm plants would help but the problem is they will take away ammonia and nitrates so youll never know if your cycle completed if theres bacteria in the tank or if your filter is just the plant make sure if you have activated carbon you change it every 4-6 weeks (reccomend 4 weeks)
if the carbon gets to old it will release all the toxins it has absorbed back into the water there for polluting your water and if you dont have fish i really reccomend fishless cycling because i find it easier in forgiving errors and if you can get filter media or gravel from another tank (filterfloss, sponges) you can go to your lfs see if they'll sell you some used filter floss from a oscar tank or chilcilds since there very messy if they wont give you the filter then ask them if they could give you some filter floss squeezing or sponge squeezings Good luck and sorry it's so long trying to help you
Reccomend a 30G aqueon filter
Fishless cycle web sites
http://www.aquariumadvice.com/forums/f15/fishless-cycling-for-dummies-103339.html
Fishless cycle data
http://www.thetropicaltank.co.uk/flc-data.htm
http://thegab.org/Water-Quality/fishless-cycling-data.html
Good luck if youre getting ammonia make sure shake it if it foams but it back its no god it has to say clear ammonia or pure ammonia only ingridents should be ammonium hydroxide and water there should be no phosphates itll help you know the ammonia concentrationtoo if you do know it just go to google and google ammonia caluclator for fishless cycle and you should be fine once again for the last time good luck i hope i helped