Help! Injured Fish From Filter Intake!!

I have a 20 gallon freshwater aquarium and it's completely cycled and I finally introduced two dwarf Golden Honey Gouramis with 2 cory cats this saturday. My Gouramis have been amazing. They adjusted so well and have been exploring. Today, I was sitting in front of my tank and saw one of my gouramis struggling at the in take of my filter. I immediately turned the filter off and he swam free only to fall to the bottom. He can't seem to swim up right and gets tired after a couple of seconds. I'm freaking out because I've only had him for a couple of days and I don't know what to do to help him. He'll lay upside down at the bottom of the tank before trying to dart to the top to get some air because gouramis like to hang out at the top.
I didn't know what to do tonight, so I turned out all the lights so it was dark in hopes that he might calm down. What do I do to help? And if I can't, how can I prevent this from happening again?

 

Did he seem to have any issues?
Ammonia?
Nitrites?
Nitrates?
Temp?

A healthy fish shouldn’t get sucked up by a filter.

 

Check your levels as suggested by 75 gallon Discus Tank above. That sounds a lot like the behaviour of one of my Cherry Barbs right before I found him at the bottom of the tank. Do a partial water change. Also, I thought you could only keep one Dwarf Gourami per tank. Have they been fighting?

Edit: Even though it is probably not the problem, I thought I would add that you can get filter intake covers on Amazon pretty cheap. I had a similar problem with my Betta's fins getting sucked into the intake. But they are slow and lazy and known to do that. I don't think it's normal for a healthy Dwarf Gourami.

 

Did he seem to have any issues?
Ammonia?
Nitrites?
Nitrates?
Temp?

A healthy fish shouldn’t get sucked up by a filter.

Not that I know of. Like I said, I just got him a couple days ago and have been monitoring it pretty closely. He's seemed very happy up until this point.

 

What about the parameters?

 

Check your levels as suggested by 75 gallon Discus Tank above. That sounds a lot like the behaviour of one of my Cherry Barbs right before I found him at the bottom of the tank. Do a partial water change. Also, I thought you could only keep one Dwarf Gourami per tank. Have they been fighting?

I thought so too, but honey dwarfs seem to be pretty docile. They haven't been fighting at all. Kind of stuck to each other's side since being taken from the LPS. It was kind of cute lol

 

What about the parameters?

That I'm not sure of. I haven't checked in a while. I'll definitely do it ASAP. I'm still new to keeping an aquarium. Thank you, I'll keep you posted.

 

An update:
My fish unfortunately was dead when I found him this morning. I feel really bad because my two golden honey gouramis always swam with each other and never left each other's side, so now my other gourami is in hiding and I haven't seen him since last night. I don't want to buy another gourami in the chance they hate each other lol.

Here's my levels as of this morning.
PH- 7.2-7.6
Ammonia- 0
Nitrite- .25
Nitrate- 5.0
Temp- 78 F

Feedback is appreciated!

 

Nitrite shouldn’t be that high in a cycled tank.