Join Date: Aug 2012
Location: Ann Arbor, MI USA
Are you using tap water or RO? I googled NYC water and it looks like GH is usually 4-5 according to google, which should be ok but might be worth checking. Otherwise not sure.
It also may be worth checking your KH, from the same sites it loks like NYC water usually has a KH of around 2 so pH of 6.4 would ballpark you around 25ppm CO2, decent but not pushing the envelope.
I would try to figure out the lighting and measure the GH. If all the easily measurable variables look good then start pushing the one that is much more difficult to measure, CO2, and assess for change in plant growth and fish behavior.
I may be missing something but that has been the one of the things I've picked up from some of the gurus. If all of the easily measurable stuff looks right and your lighting situation is appropriate the issue is probably the CO2 (though I wouldnt think this would affect the floaters).