As to why you are getting streaks now, its because the Jobo tanks are not made to be used the way you're using them. When you have the single tank full of chemistry you are not able to get even agitation. You're probaly not getting much exchange no matter how you agitate. The single tank is too full when the film is covered completely in developer. Its really made to be used on the revolving processor with much less developer. The extra room in a larger tank will let you get good, even agitation by hand.(posted 8147 days ago)So, what you need is another tank. The Jobo 2551 is made to hold two 4X5 film reels. Buy one of these. Fill it with developer to a level slightly higher than the height of a single 4X5 reel. Then with the lights off transfer your loaded reel (you already loaded it and placed it in a capped single tank) from your single tank into the 2551, clip on the top and start initial agitation. A continous gentle swirling or rolling will do. Or if you can keep the lights off you could raise and lower the reel, then clip the top on and work in light for the balance of the time.
A single tank is not deep enough to allow you to cover all the film even when filled to overflowing with the top off so you can't prefill a single and get nearly instant coverage/wetting of the film. Pouring the large quantity of developer needed to fill the tank takes too long and is one cause of your problems. Thats another reason why you should buy the double tank and pre-fill it. When you place the film in the pre-filled tank it is instantly covered/wet by the developer. You can continue to pre-soak your film if you like before transfer to the developer filled double tank. You might want to use another reel on top of the loaded one to be sure it stays down in the developer, or make a spacer to do this.
I'd agitate the double tank by rolling it one or two gentle revolutions on its side each 30-60 seconds, then standing it upright. Be gentle! Too vigourous agitation might dislodge the film from the reel. A liter of chemistry sloshing around in a 2 liter tank can have a lot of force against the sheets of film.
Alternately, you could turn off the lights each minute and lift the film out of the developer then set it back down. Or leave the lights off and raise and lower the film as needed. Have your stop and fix in containers ready to pour in the tank.
Pouring all your chemicals with the cap off, in the dark would be great! (although probably not necessary, it might be better) I'd stop with plain water only and roll the tank continously for one minute, drain, lights off, cap off, then pour in the fix, cap and roll for first minute, roll occaisionally through the fixxing time.