Even in our recirculating 16 bucket system which uses around 70 gallons water, we have to balance the pH everyday. If you start with 6.8-6.9 pH water like we do...its a constant battle. But on a smaller system, yeah twice a day is nothing, I could see even more. When I used to do single 20 gallon tubs, they had to be pHed 2-3 times a day.

Ive started using Advanced Nutrients pH down and its been great, keeps it for longer but more specifically... it barely takes a teaspoon to drop our 70 gallons more then 2 whole points (like from 7.0 to 5.0). When your pHing everyday, saving money anywhere you can is great. Make sure you have some pH up though cause its way way way easy to overdo it, especially on a small system. Youd use a couple drops!!