Change foreground brightness & weird bug with num of LEDS

[Wail3Y]

I am using WS2812b's connected to an arduino which are powered by 5v Molex on my ATX Power Supply.
There are 75 LEDs in total stretched across 2 strips. The issue is, the strips are really spread apart so resistance is super high. The 60 LED strip doesnt get enough current so I turned down the background brightness to prevent the colours from messing up, but the foreground brightness is still the same so the whites are red and the other colours are washed out too.

Another thing is, when I try to set the num of LEDs to 75, the colour sequence buggs out and i have a vomit of colours all over the strips but when I set it to 74 everything goes back to normal.