When you get ready to run and want to keep a light load and no water, put the valve switch to "recirc". This closes the valve to outside water.
When you get ready to put fish in the livewell, switch the valve control to "Auto" or "fill". I'm not sure what it says on the Nitros now. But it's the only other one from "Recirc" This will allow it to open up to pull watet in. Then put your aerator switch (toggle switch) to "Fill" or "manual". Again, not sure of the nomenclature, but it should read one of those.
Once it's full, switch the toggle switch (not the valve) to recirc. It will pump fresh water (because your valve is still on "fill" or "auto") every minute or so. You should have a timer that allows you to adjust the frequency and duration of the cycle. I always max mine for the health of the fish.
Whenever you get ready to run, switch the valve control to "recirc" to hold the water in or else it will drain while you run. This closes the system off to outside water. Since my toggle stays on all day, I don't have to turn it back on, but during runs, I switch mine (the toggle switch) to "Auto" or "Manual" so that it recircs constantly during any run and keeps O2 in the water. I also use a bilge plug to stop up the overflow in the livewell so no water runs out.
Then once you get to your next spot again, switch the valve back to "auto" or "fill" to bring in fresh water, and the toggle switch to "recirc" so you don't kill your battery.
Now a few tips:
If you're catching fish up shallow in muddy, warm water, when you run to another spot or to weigh in, it's always good to stop out in the middle of the lake where the water is the coolest, cleanest, and most O2 rich and fill the wells with that water. It's better for the fish.
If you have good cool water with release agent in it and run to warmer water, that you don't plan on being in for more than a few hours, it may be best to NOT switch to outside water and just keep recircing whats already in there. Make sense?
A lot will depend on how many fish you have in the wells and the size. Say you have just a limit for you of 5 small keepers that weigh collectively 12 lbs. Well they will require much less O2 over the course of the day than say 2 limits (you and a partner) of 10 fish total that weigh more on average as well and you have 32 lbs of fish. They also will release a lot more nitrogen into the water. This is why changing water out completely is very important.
If I'm fishing the main lake, I will pump fresh water in every hour and replace my release agent when the water turns clear. And if the water is especially warm, I will also use ice on occassion to cool the temps down and slow the fish's metabolism.
Hope that helped. It's harder to explain in type than it is in a boat.
, I make sure the valve for that livewell is on fill and turn the left pump switch for that livewell on manual (press down). When that livewell gets full (water level with the smaller opening), I shut off the pump switch that is on (middle position) and turn on the right pump switch for that livewell on auto (press up). Also move the bottom valve control for that livewell (recirc./pumpout) to the recirc. position. If the first fish is a big one (over 4#) or when I catch my second keeper
