Sorry - I can't advise you on that product because at least here in the US, I'm not able to find what the dose of praziquantel actually is in that product.
I found a web page that says that this product contains 66 mg praziquantel per ml. I cannot say if that page is accurate or not, but the full single dose for praziquantel is 2.2 mg/l. The day one dose that they show would contain 253 mg of prazi. To dose 30 gallons of water at 2.2 mg/l, you would add 250 mg of prazi. So - their day one dose is essentially a full dose. You should dose just that, and then 7 days later, dose it again, and 7 days after that dose it a third time.
Because it is a liquid formulation, it has some solvent in it, and you would need to know what they use for that.