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Betta are, unfortunately, unpredictable creatures. Sometimes they are fine with tank mates; sometimes they're not. And, sometimes they'll do great and then change overnight. The latter even happened with one of mine who had been fine for two years with other fish.
To help, and even if you have live plants, I would turn the lights off for three or four days. This is calming to both your Betta and the Cory and give each some "breathing room."
Cory are shoaling fish and the minimum number of shoalers is six. Pet stores and some online sellers will tell you three or four is enough. Not so. Rachel O'Leary (msjinkzd on YouTube) is one of our leading authorities and lecturers on aquatic life. She's studied and written books on Nano fish. She says no fewer that six because, for shoalers, there's safety in numbers. So I'd add get more Cory while the lights are off.
Artificial or real, I would add at least 50% more plants. Betta are shade- and cover-loving fish and some can become stressed if the tank is too open. This is an artificial plant I recommend. It is soft plastic https://www.chewy.com/marineland-bamboo-aquariums/dp/133090. You can get it anywhere; we just happen to use Chewy.
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Here are a couple of tanks with the Bamboo. Let it flow over the surface of the water to give your boy some shade.
I doubt it's the filter that's bothering your boy and keeping him at the bottom unless it is so strong there's no place calm enough for him to swim, rest or eat without being bounced around. I can't tell what kind of filter but if it's one of those that hang on the back, you can suction a plastic soap dish under the filter's output.
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Some people add colorful glass.
If your tank has a lid you can raise the water level to the bottom of the black rim. You can cover any openings with plastic wrap or craft mesh. Even an additional inch or so would give him another gallon of swim space.
Now, how's that for TMI?
Oops, almost forgot: How did you cycle your aquarium?
Betta are, unfortunately, unpredictable creatures. Sometimes they are fine with tank mates; sometimes they're not. And, sometimes they'll do great and then change overnight. The latter even happened with one of mine who had been fine for two years with other fish.
To help, and even if you have live plants, I would turn the lights off for three or four days. This is calming to both your Betta and the Cory and give each some "breathing room."
Cory are shoaling fish and the minimum number of shoalers is six. Pet stores and some online sellers will tell you three or four is enough. Not so. Rachel O'Leary (msjinkzd on YouTube) is one of our leading authorities and lecturers on aquatic life. She's studied and written books on Nano fish. She says no fewer that six because, for shoalers, there's safety in numbers. So I'd add get more Cory while the lights are off.
Artificial or real, I would add at least 50% more plants. Betta are shade- and cover-loving fish and some can become stressed if the tank is too open. This is an artificial plant I recommend. It is soft plastic https://www.chewy.com/marineland-bamboo-aquariums/dp/133090. You can get it anywhere; we just happen to use Chewy.
Here are a couple of tanks with the Bamboo. Let it flow over the surface of the water to give your boy some shade.
I doubt it's the filter that's bothering your boy and keeping him at the bottom unless it is so strong there's no place calm enough for him to swim, rest or eat without being bounced around. I can't tell what kind of filter but if it's one of those that hang on the back, you can suction a plastic soap dish under the filter's output.
Some people add colorful glass.
If your tank has a lid you can raise the water level to the bottom of the black rim. You can cover any openings with plastic wrap or craft mesh. Even an additional inch or so would give him another gallon of swim space.
Now, how's that for TMI?
Oops, almost forgot: How did you cycle your aquarium?
