You mix 6 scoops with 900ml of water then, when it's completely mixed, you top up with more water (if needed) to get 1000ml total of mixed solution.
As for dosing... Start with half the recommended dose (5ml AFR for every 26g of actual water volume). Test ALK daily while you get things dialed in. Dose the same amount for AT LEAST 3 days at the same time of day before making any changes. After 3 days, adjust your dose up or down as needed until you get 3 days in a row where your ALK doesn't change. That's your starting dose.
It's helpful if you try to test at the same time of the day and dose at the same time of day (not necessarily the same time). When I started I was manually dosing once per day. I tested ALK at 8:00am, then dosed when the lights came on at 8:30am.
As a side note: You certainly CAN dose manually once a day, but I saw more more stability once I put it on a dosing pump and split it into multiple smaller doses. I also had to dose a bit more (daily total) once I split it up over the day/night. I currently have mine set to dose every 2 hours, all day and night.