That bottle has a an odd shape so you can't just divide it by 4, I would weigh that one empty and note the weight, then fill it with water to bottle weight + 500 gram, then dose 125 gram of that each day.
True! I honestly don't know how I did not think about it lol. So I put in tank water to the 500ml bottle, then I put in 5ml and shake the bottle and then I put in the 125ml of the mix to his tank?
No use tap water or whatever water source you use to change water. Put 500 ml (ideally 495) in the bottle (or 4 times 125 if that is the size of the cup) + the 5ml.
Shake before dosing 125ml of that in the tank.
If it is bacterial it could possibly help. If not.. there isn't much more you can do.
So I use tap, I put tap water in the bottle and then I put in the 5ml of Artemiss to the bottle and shake well before dosing 125ml to the tank? I hope I got it right...