And not enough flow/circulation. They usually grow because of silicates in the water which is especially true if you’re using silica sand as substrate. Too much nutrients and nitrates and/or low oxygen content can also be the cause.
It’s been set up for 3 and a half monthsHow long has the tank been set up? That looks like diatoms, which almost all new tanks get.
Is it usually difficult to rub off? I usually have to scrub it with brush.
If it sits for too long then yes it can especially on the tank walls. I usually rub them off as soon as I see them. If that doesn’t work and it’s stubborn, a clean and unused toothbrush will work just fine. It’s what I use to clean rocks, filter parts, plants, etc.Is it usually difficult to rub off? I usually have to scrub it with brush.
I was afraid to try live plants for the longest time. Now I’m converted and I don’t think I’ll ever be able to go back to fake plants! Caring for them sounds so intimidating, but really it’s as difficult as you make it. I’d recommend just dipping your toes in and buying a couple easy plants instead of going all in at once. You can have an easy setup with a few plants, some fertilizer, and a basic tank light. Java Fern was my first and is my personal favorite. Looks great, nearly impossible to kill, doesn’t need any special care. But in general, if you Google “Easy aquarium plants” you’ll find a nice selection of beginner plants to get you started.I’m thinking about getting live plants soon actually. Do I need special gravel/sand for them? If you want I can create a new post for this.