So the tank just over 17 gallons.
Added to many fish to soon.
I would preform a water change.
If you don't have a airstone lower the water level so the filter hits the water harder.
Is it possible to load some pics up onto the site so we can see the fish you don't know what they are.
Buy a master liquid test kit in ammonia, nitrite, nitrate, and ph. The api master kits is a good deal.
1. do a 10-15% water change daily.
2. continue until ammonia and nitrite are at 0 ppm.
3. Test water daily for ammonia and nitrite until holding at 0 ppm. If high do an immediate extra water change.
4. Keep bubbles going.
5. Avoid medicines.
6. Keep plants.
7. If high, don't feed fish, if do, only little and clean after.
8. Wash filter in tank-water.
Should I follow that or could I contact you when I've tested the water of instruction as you seem to know what your doing.
The stripey fish is a danio. Is there a red patch near his eyes.
Not sure what plec or algae water that is. Post the pic of him in tropical discussion.
Only thing you touch in the filter is filter floss. Is white matting and need rinsing or replacing once a week.
Don't touch the sponges at all till the tanks cycled, Then you only rinse one sponge in old tank water if it's really mucked up., then do the other sponge a few weeks later.