Just getting started, it’s going to take you awhile to get through 3L. You want to build up to the recommended dosage allowing zooplankton time to respond accordingly. Keep in mind this is adding nutrients to your system so balance is important.
Once it reaches the color target, or the population is dense, then the culture should be refrigerated. It has to be turned daily, but otherwise, I’ve had it last 45 days before using it to start another culture. If it’s kept at room temp, I would expect not much beyond 14 days but that’s guessing. When it does crash, it happens fast.
We manually add phyto as part of our daily maintenance plan. We’ve also used it to grow our own Pod cultures. Combine 1gallon phyto to 3gallons of water, buy a 16oz bottle of Pods from another hobbyist, add an air stone & wait 20 days. Live food!
I’ve seen a few threads from people that have designed auto-dosing mechanisms for this, but that seemed like more work than I’m willing to invest.