If you are looking to dose something into your sysetm and done the proper research to guarantee thats what you want to do than what you should do moving forward is do some reverse math work to get the proper amount for your water volume.
You would not want to do the 1ml for the 25G because your system is about half that, and dont forget to factor in rock and sand which will lower the total water volume. You probably could get away with a half dose if that is your end goal to use this product.