Hello again (good pictures you’ve taken there BTW),
OK, these are just my opinions on what I’ve read thus far..
Stocking
Stocking based on the general rule based on the surface area of the water in your tank which is 213 square inches yields a total mature maximum stocking length of 18 inches. Stocking based on the general rule based on the volume of the water in your tank which is 16 US Gallons yields a total mature maximum stocking length of 16 inches.
Adding up the stocking you currently have, yields a total maximum mature length of approximately 45 inches. Your tank needs to be at least 2.5 time bigger, but I think you know that anyway. For good general information on fish species, see this link to the forum’s ‘Fish Index’:
http
/www.fishforums.net/index.php?showforum=36
Simply considering just the maximum total stocking length is not the end of the story – it is more complicated than that when stocking a tank (things are always complicated for some reason): Many fish like to be in minimal groupings of 4 to 6 individuals. Also, many fish (regardless of inches / per US Gallon rule) need minimum tank sizes. Finally, careful choices must be made when choosing tank mates. This is why you may see many threads regarding advice on stocking options.
OK, your fish are not yet fully mature – add up there current lengths and see if things are OK NOW. Then plan for the future when they DO start to out grow the tank. If you are worried about current 'baby' sized stocking levels then perhaps consider adding a second filter. (Many people add second filters to their setups regardless). Perhaps use your old filter as well, if you have not thrown it away?
Oops
As you know, a tank needs cycling, i.e. time for the nitrifying bacterial colonies in your filters, substrate, stuck to your glass etc to build up to a level that can cope with the amount of Ammonia & then Nitrite that a certain stocking of fish produces. Regular water changes then take care of any Nitrate. If you have fish in a tank then you are going to have some levels of Ammonia, Ammonium, Nitrite and Nitrate in your tank.
You don’t HAVE to have 0 levels of everything. I consider these ranges:
(
Toxic) Ammonia – >0.02 – very dangerous (I’ll come back to this)
Nitrite: less than 1.0ppm Good, 2.5ppm Liveable, >5.0ppm, worry, do water changes etc.
Nitrate: <40ppm ideal. >100ppm, worry, do water changes etc.
If you are saying:
‘Ammonia’ = 0.1ppm <- this is a measure of Ammonia AND Ammonim.
(Actually 0.0000277ppm TOXIC Ammonia)
Nitrite = 3ppm getting nasty – do some water changes to bring this down to below 1ppm
Nitrate = 2.5ppm well within safe level
PH = 6.4 fine. <- investigate your fish on the ‘Fish Index’ or where ever to see what your fish prefer. BTW, I guess your tank is now going through a cycling process. During this pH will go all over the place. Trying to set your pH by adding stabilizers will be foolish and unnecessary.
Temp 24°C fine – increase it to 27°C – this will speed up the cycling process.
(BTW, do you use drop test kits?)
As you may well know, I think your tank is cycling again because you switched filters. This is bad news really especially considering how over-stocked you are. If I were you I’d seed your filters with Mulm.
Mulm
Deep vac your substrate. Let the water you’ve collected settle. The crap settled in the bottom of the bucket is Mulm. Carefully drain the water out, collect this stuff and add it into your filters, hence seeding them and thus greatly speeding up the cycling process.
If I were you, I’d consider daily 20 to 30% water changes until your tank gets re-cycled. This should take care of your now rising levels of Ammonia, Nitrite and Nitrate. Test daily for levels and act accordingly. Water changes will not affect the bacterial levels as these bacteria are sessile and are not ‘in the water’.
I suggest water changes over adding Prime because it is cheaper and in adding Prime you are taking away the exact thing that your filter need in order to cycle, i.e. food in the initial form of Ammonia and Nitrite!
As I suggested above, increasing the temperature of your tank will also speed the cycling process.
The Ammonia / Ammonium Balance
The lower your pH, the better with regards to TOXIC levels of Ammonia. I am not a great believer in ‘fiddling’ with pH. If you are going to take this route then start with RO (Reverse Osmosis) water and go from there. I do not know why it has been suggested that you HAVE to aim for EXACTLY a pH of 7.0…..
Your test kit measures ‘Ammonia’, i.e. NH3/NH4, in other words it is simultaneously measuring a combination of TWO things, toxic Ammonia and (safe) Ammonium (Note: both Ammonia and Ammonium get eaten by the nitrifying bacteria). The lower the pH, the less the balance swings towards toxic Ammonia, so in this respect a low pH is very good.
See here:
http/www.fishforums.net/index.php?showtopic=154313
Ammonia (NH3/NH4) = 0.1ppm, pH=6.4, Temp = 24°C Yields: 0.0277%, i.e. your actual TOXIC levels of ammonia are 0.0277% of 0.1 = 0.0000277ppm. In other words a factor of 700 times below that considered dangerous, i.e. 0.02ppm
Chemicals
I wouldn’t blanket state that adding ‘chemicals’ to the water per-se is bad. Some ‘chemicals’ are definitely required, such as water conditioners that remove chlorine, chloramine and heavy metals from tap water. I also dose fertilizers for my plants on a daily basis.
I do not believe in bacterial cultures – I think they are a waste of money (with the possible exception of BioSpira) – if these products do not come refrigerated or fed / aerated, then I cannot see how they can live. (BioSpira is the only product that I know of that is refrigerated).
BTW, an air-stone IMHO will do next to nothing with regards to oxygenating the tank and should NOT be used in a planted tank as it will reduce levels of CO2. The output from your power head should be positioned such that it ‘gently agitates’ the surface of the water.
White Spot
I don’t think bad water does not ‘causes’ white spot per-se. However, it does not help matters as it does reduce the fishes immune system and makes them more susceptible. The white spot must have come from some where, & I’m guessing that you have recently added new fish and that is the source of the disease. White spot is now in your water and in this respect your water is now ‘bad’. This is why it is always recommended that if you can, new fish should quarantined. Quarantining any sick fish is also the done thing in an attempt to prevent the disease from spreading form fish to fish. Hospital tanks are also smaller and therefore cheaper to medicate – but of course they will not be cycled so are higher maintenance: you want this water in tip top condition to aid the fishes immune system and thus speed recovery.
Honestly, GL
Andy
. We called him lightning maqueen like the character out of the new disneys film cars. He zooms around and jumps out of the water.. he cracking! 
