Now, one of the largest I've seen for sale in a pet shop(Not here, in the US) was a tank full of little 150ish mm Arapaima Gigas, They were about $20 iirc.
Judging from it being Livingart and the glass in one of the pictures I'm reasonably confident that he has kidnapped them from the wild and imprisoned them in some kind of tank or terrarium so they are no longer in a garden.
He just had too much, lost all his friends and family when he was kidnapped by a stranger and forced to live in a wierd new place. May you should get him some professionals to help him deal with it before he does manage to get through the silicone and drain the tank. Suicidal fish is a serious and often overlooked issue.
Wooohoo, I can put a full grown pacu in my tank, they're only 100cm or so, I'll have another 10cm of fish I could in even.
A little plant and a couple leopardfish fry would probably work well. Maybe a betta.
I'd think you'd be better off with a couple big pumps if, like it sounds like, you're running them off a big sump. How much flow at 2M are you wanting?
Horizontal is better because you can put it lower so it doesn't come out of the water during water changes and gives microscopically better heat regulation.
Also if it's a long heater it can fit better than vertical.
In the case of my tank it's diagonal because the cord isn't long enough to have it low in the tank and horizontal.
You don't have to. I only boil it because that way it sinks and I don't have to try to weigh it down.
I put it in big container in the microwave and boil it for about 5 minutes.
For the single bristlenose it looks like you have, maybe a single slice a couple mm thick every day or two.
I dunno if there is an even newer model of the CF1200 that has a primer. But I have an "Aqua one" and an "Aquis" Both are identical other than the label.
Primers are a waste of time. Other than when you first install the plumbing or remove it is the only time you would use one. And a quick suck on the hose and will work far better. Most primers I've seen are useless anyway.
Even if you do a water change with some water that doesn't have any dissolved O2 any reasonable amount of airation should bring the level up again within minutes or an hour at the most.
That's why you should always make up little containers and say "Dump in one per day." Having some random noob feed your fish is nearly guaranteed to get them killed.