After using the same tank and reels for years, I seem to be having problems with development. I've changed everything around. Cameras. Film. Developer. Same problem: uneven, or under development at the edge of the film. (the film has small oblong clear marks). I've just done about 16 rolls of film all the same way with the same developer. Same agitation. All strictly uniform. Everything is pointing to the tank and reels. Is this possible?