Explanation:

Biofilters do not remove uneaten fish feed. The physical removal of solids such as uneaten feed is typically accomplished through mechanical filtration, not biofiltration. Therefore, this statement is incorrect.

Biofilters convert ammonia present in fish waste to nitrate through a process known as nitrification. This is achieved by the action of nitrifying bacteria. Thus, this statement is correct.

Biofilters do not increase phosphorus as a nutrient for fish in the water. Phosphorus is typically managed through other means in aquaculture systems, as it can lead to algal blooms if concentrations become too high. Biofilters are primarily concerned with nitrogenous waste (ammonia, nitrite, and nitrate). Therefore, this statement is incorrect.