GH and KH are sure at the low end of OK, great for soft water fish!
Otos should work. They eat the flat, stuck-on sorts of algae, not stringy algae.
You will have to research shrimp, find out which ones are OK with that soft water. Some Bettas are quite predatory and will eliminate all the shrimp. You might get a few of the cheapest to see if he is OK with them.
I would be concerned about zero NO3.
The plants are using all the nitrogen you are adding. Or else the test is not working.
Otos should work. They eat the flat, stuck-on sorts of algae, not stringy algae.
You will have to research shrimp, find out which ones are OK with that soft water. Some Bettas are quite predatory and will eliminate all the shrimp. You might get a few of the cheapest to see if he is OK with them.
I would be concerned about zero NO3.
The plants are using all the nitrogen you are adding. Or else the test is not working.