I've got my wee tetra here who has had this white growth on his mouth for a week or two. He's been treated with API Melafix and anti bacterial and fungus treatment, but the poor guy still has it. I've attached pictures. Anyone know what it is, and/or what could help?
Yes, its the only one currently affected. Nitrite and nitrates have all been very low/if any and the water regime at the moment is 25% after 7 days. As per the anti bac treatment. Before then it was as and when nitrates got up, so every 2-3 weeks?
You don't mention ammonia which is a crucial test. This makes me wonder if you're using test strips which don't contain the crucial ammonia test and that are much less reliable and specific than liquid-based tests. Essentially, most health problems in fish are caused by impaired water quality - and it's essential that ammonia and nitrite remain at 0 at all times (not just 'very low') and nitrates less than 20 above whatever your tap water nitrates test is.
I would advise: * buying a liquid-based test kit (eg API Master Test Kit), if you don't have this already, so that you can monitor these at least weekly before your new regime of a 25% water test every 7 days; * even if ammonia and nitrite are 0 and nitrates <20 just before the proposed scheduled water change, still do a weekly water change as described - water contains all sorts of other things including buffers for PH and fish stress hormones, some of which can't be tested by any test, but replenishing the water weekly ought to address these; * if any presence of ammonia or nitrite, or higher nitrates than described, then do larger and/or more frequent water changes; Hopefully this ought to resolve the problem in time.
If this doesn't address the problem, it's worth checking out that your water hardness/softness level is suitable for the fish. Neon tetras require water of 18-215 ppm/CaCO3 which equates to 1-12 dH (German degrees hardness). If your water is too hard for them (your water supplier website should give details of your water hardness for your postcode using these measures), then there are ways of addressing this - but it would depend on what other stock you have.