Well my tank is 75 liter. I'll ask her which size tank she wants, refills will be more often and so probably more money, a 5 lb tank is about $50 a 10 lb is about $80 so only $30 more for twice the size. What regulator would you suggest? I told her I would go ahead and order everything, only thing i need the thumbs up on is CO2 tank and if she wants inline atomizer or pollen diffuser. Don't think she really liked the micro bubbles. Is a Ro/DI system a good idea?