Using more than the stated 290 ml is generally fine. That figure is the minimum needed to cover one 35mm reel, not a strict maximum.

In practice, many people use around 500 ml in a Paterson Universal tank, especially if it’s the type that takes two 35mm reels or one 120 reel. Extra developer usually won’t hurt results as long as you keep the dilution, time, and temperature correct.

What does matter is having enough active developer. If you use too little solution, development can become uneven or stop before completion. This is especially important with very dilute developers or stand development, where the minimum amount of stock developer may be too low even if the film is technically covered.

A good approach is to measure how much liquid your reel setup actually needs to fully cover the film, then round up to a convenient mixing amount. If using one reel in a larger tank, an empty second reel can help keep things positioned consistently.

So: 290 ml is a minimum fill level. Using 500 ml is usually fine and can be preferable.