Long streaks running along the length of 35mm film are most often caused during the final rinse/drying stage, not by the reel height in the tank. The most likely cause is too much wetting agent in the final rinse, which can dry as residue and leave flow marks.

First try a simple fix: rewash the film, then do a final rinse with the correct wetting-agent dilution and hang it to dry again.

If the marks remain, one answer suggests re-fixing for about twice the normal fixing time, then washing and doing the final rinse again. That said, fixer problems usually don’t produce smooth flow-like streaks.

Poor loading on the reel can cause development problems too, but it more often creates uneven patches or undeveloped bands where the film touched or overlapped, rather than long drying streaks.

So the most obvious thing to try is a careful rewash and correctly mixed final rinse. Also make sure the film hangs cleanly to dry and that your wetting agent is measured accurately.