I think the sera liquid fertilizer is Florena. Which is quite a good product. You can dose the fertilizer. but don't over dose. follow the instruction on the bottle and figure out how many liter of water do u have.

your otto and shrimp dying due to high temp. (just my guess) coz i hv a shrimp tank and was forgotten to turn off the lighting for 3 days. End up all the shrimps inside there died.

try to get a fan blowing to the nano tank. Riccia can't do well in high temp. They are sensitive to water as well. Try to change 30-50% of water weekly. Higher temp might easily cause the algae problem.