If i'm correct you should add 0.5 mL to your 1 gallon tank, and I would say about 1.25 mL to your 2.5 gallon. It will not be extreme if you end up putting a little more in than you are supposed to. I'm not 100% because i haven't slept so my brain is being slow.
Answer:
100+x
Step-by-step explanation:
Peter starts out with 100 dollars and then gets X more meaning we have to add X to what he originally had and that looks like this 100+x
I hope this helps and please don't hesitate to ask if there is anything still unclear!