Problem 1. Pipe threads are tapered. They are designed to wedge tightly. Use a wrench. Not a whole lot of torque, but more than just hand tight. And use teflon tape on the threads so they slide easier.
Problem 2 Leave everything alone and concentrate on maintaining 16 FC.
Problem 3: your filter is working as designed. What is happening is that you kill some algae with your weak FC, but what remains grows. So you have an endless supply of dead algae to clog the filter. Once you get ahead of its growth, the intervals between clogs should get longer and longer.
Problem 2 Leave everything alone and concentrate on maintaining 16 FC.
Problem 3: your filter is working as designed. What is happening is that you kill some algae with your weak FC, but what remains grows. So you have an endless supply of dead algae to clog the filter. Once you get ahead of its growth, the intervals between clogs should get longer and longer.