Dark & Light Spots on Negatives

[MattKing]

For clarity, the modern Paterson tanks have a screw in top with a built in large funnel which also serves as an air cavity.
If you fill the main lower part of the tank (not the funnel top) to the brim, they work great.
If you fill the complete pair (lower part and screwed in funnel top) to the brim, there isn't enough air, and they work poorly.

 

[Bill Burk]

Because there are so many people using Paterson tanks .
More usefully, it is because the Paterson tanks that people have and use are very flexible, in that they are designed to be able to be used with a variety of sizes and quantities of film, so the possibility off using them with either too much or too little developer is very real.
The old Paterson System 4 tanks didn't build in space for an extra amount of air above the liquid, so one had to be extra careful to get the volumes right.
~35 years ago the people at Paterson realized the problem, so they replaced that design with the Super System IV.
If you (over) fill one of those to the brim, you will be using way more developer than necessary, the lack of air in the cavity providing for it will inhibit correct agitation, and you will greatly increase the chance of leaks.

Fair.

How about the reels slide up the core? That used to happen and the clip didn’t help at all.

Is there a spacer that people can use to keep the reels from sliding up or do the new ones “not do that”?

If that’s an issue still, I could change my recommendation to say “fill up enough to touch the funnel”.

If reels don’t creep up, I’ll be a monkey’s uncle.

Last weekend playing spite and malice my cousin and I were showing six 7’s and I said if mom turns over a seven I’ll be a monkey’s uncle and she did. So I have been one before.

 

[MattKing]

My AP Paterson clone reels don't seem to slide - I don't feel or hear them doing so - but I don't much care because I always fill my 1 litre Paterson tanks to 1 litre (with replenished developer), and I always put one or two empty reels into a tank above the full reel when there is room.
I also use continuous rotary agitation for almost all my developing.
FWIW, a fairly large percentage of my Darkroom Group use modern Paterson tanks. And as a result, I regularly see a lot of developed negatives, from a decent number of photographers. Some use rotary agitation, while many use inversion agitation, and aside from some rare and unusual circumstance (eg old film sizes in converted reels), don't see such problems.