Just calculate the net total volume and adjust your dosage. Its harder to dose small tank volume with the drop but u can adjust the day. Example 1 drop per 25g per week for your tank you can do 1 drop per 10 days.Picked the Starter Package and a bottle of Sponge Power during the BRS sale. I been reading a lot on Zeo, created a spreadsheets to track dosing but have to deal with dino or diatoms first. If everything goes well in a month or two might start dosing. Tank is a small IM20 gallon.