FYI, if your tap water is not too hard I would suggest you just run tap water throgh it (measure it by gallons though, don't just turn the faucet on your plants) and just run gallon after gallon through it.

Then in the last 5-10 gallons start PH'ing your water to 6.5. This helps speed the process up SLIGHTLY.

You have 30 plants, you're going to be flushing for a long time. I only had 5-6 plants last time and it took me 1-2 hours for each plant.