Water Changes Question

[Davo86]

It probably is 350l, either that or 190l but if it is fluval then it will be a Venezia which definitely only comes in these two sizes.

 

[ColR1948]

Tested the water this morning, I still have a small trace of Ammonia, not really on the colour chart as it is lighter in colour so I'm guessing around 0.3 if that.
I did use Seachem Prime and I read somewhere it can give a false positive as it reads Ammonium, I may be wrong here so please correct me.