Edit..it could be from being in the previous tank ,especially if they were not kept properly High Ammonia can cause long term problems well done for giving them a nice home and good luck.

So, I would move them to the koi pond asap.

Now, they could be sitting on the gravel for a few reasons

1) They’re tired
2) The water quality is bad
3) They’re sick

I’d get a lid, you may come home one day and find a dried goldfish on the floor.

Secondly, 3 pellets a day is fine.

Thirdly, you need water conditioner, also known as dechlorinator, to remove the chlorine and chloramine from the water. You can’t just let it sit and evaporate out like some people say you can, because, chloramine NEVER evaporates and is also toxic like chlorine.

Betta fish are pretty small, they only get an inch or two long (their body without the fins) max, so, yeah.

Fourthly, don’t get a female betta for him! Breeding bettas is the only time when they should be together. Even when trying to breed, then will fight and often cause bad wounds. Breeding should only be attempted by someone who has studied how to breed them and then the process is done very carefully. If anyone tells you that you can keep a male and female betta together, you should just laugh at them, they know nothing. Only experts can attempt it. Personally I would never try it. They DO fight and often wound each other badly enough to die.

DON’T LISTEN TO PUPPYLOVECB. Bettas don’t come from china, they come from thailand, from RICE PADDIES, which are not puddles. They are shallow, but not shallower than a 5 gallon tank. 5 gallons is PERFECT for a betta. My betta lives in a 10 gallon actually and he is happy.

A betta who lays on the bottom all the time is sick or cold.

Also, bryan b’s recommendation to keep catfish or algae eaters will only make the water DIRTIER, not cleaner. All fish make the water dirtier because they create more waste. And if there is algae in your tank, you can clean it off the sides if you want, but your betta won’t care.

As for your other questions, let’s see. You use the amount of dechlorinator that the package says. I can’t tell you how much to add because every dechlorinator is different. You add it to the water that you are filling up the tank for the first time, AND whenever you do a water change you add it to the new water. DON’T add it daily.

The dechlorinator works immediately to remove chlorine from the new water. That’s all you need to do. After you add the dechlorinator to the new water then you pour it into the tank.

This is done when you do your weekly water change. You should change about 20-30% of the water each week and always add dechlorinator to the new water.