Good day I have 3 goldfish and 1 is sick, so I got some Sera Omnipur and added that, together with aquarium salt, to the tank. The instructions said to aerate well during treatment, however, the sick goldfish is too weak for the filter stream and even gets sucked up against the filter, so I decided to put it in a fishbowl (I don't have 2 tanks) and then to switch the water around several times a day (pour the bowl water into the tank and pour fresh, aerated water from the tank, into the bowl). Remember that all the water is medicated. However, the water is getting less - probably evaporation - and now I want to top it up. Can I add new water which is medicated proportionally, i.e. if it's 25% of the tank volume, then I add 25% of the medication dosage, or is medication such as Sera Omnipur supposed to be single dose, no top-ups?