Do you have a water test kit? Drop liquid tests are the best. What we need are Ammonia, Nitrite and Nitrate. Temperature would also be helpful. Anything is a guess without those numbers.

Also how many fish of each species are in the tank? How often do you do water changes and how much do you change?

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29 Gallon Planted
1 Angelfish; 2 German Blue Rams; 11 Rasbora Boraptensis; 3 Khuli Loaches, 1 BN Pleco

20 Gallon Planted
2 German Blue Rams; 5 Corydoras Paleatus; 4 Otocinclus Catfish; Amano Shrimp

5.5 Gallon
Betta, Some plants.