Is there any advice you guys could give me before placing any fish in my aquarium? There’s already water (treated) in it, filters running and I got a heater.
You need to cycle the tank.
This is the process of growing the bacteria which remove toxic fish waste. I simple terms, fish excrete ammonia which is poisonous to them. In a cycled tank there are bacteria which eat ammonia and turn it into nitrite. This is also poisonous, but in a cycled tank more bacteria eat nitrite and turn it into nitrate. This is only poisonous at high levels and we remove it by doing water changes.
In a brand new tank there are virtually none of these bacteria so we need to grow a lot more, and we call this cycling.
You can put fish into a brand new tank but this means testing the water for ammonia and nitrite every day and doing a water change whenever there is a reading above zero.
Or you can grow the bacteria before getting fish - this is called fishless cycling and we do it by adding ammonia from a bottle to simulate fish waste.
There are bacterial starters on sale but these speed up the cycle, they don't do it instantly whatever the store might tell you.
Live plants can also help as they take up ammonia and turn it into protein rather than nitrite. But looking at the photo of your tank you may not want to change the decor.
Can I suggest you read this - you'll probably need to read it a few times to get your head round it.
Cycling Your First Fresh Water Tank What is Cycling and Why is it Important? Fish waste, and especially fish breathing, plus uneaten food and other organic matter breaking down in a tank all produce Ammonia. This can quickly become toxic to fish if it is allowed to build up to any measurable...
www.fishforums.net
Then make a decision whether to do this, or whether you'd prefer to do a fish-in cycle with its daily water testing and water changes.