Nitrate & Phosphate removals

Too much nitrate (No3) and too much phosphate (Po4) are not good for a saltwater aquarium with corals. Always take a good look at your eating behavior, not too much and too often a day.
A fish eats every time the fish feed sees, this is not a sign that they are hungry, but a natural reflex. Maybe the food will not be there tomorrow, so fish grab what they can grab.

Always have a working skimmer.

Excess phosphate can be easily removed with a phosphate removal agent, these products bind the phosphate and will not let it go. Well-known products are Rowaphos and DSR PhosRem.

Silicates can also be absorbed. Excess Silicates can cause a brown algae that usually ends up on the sand.

Too much nitrate can be tackled by feeding the bacteria with a carbon source (not to be confused with activated carbon). Nopox from RedSea is a popular product for this, but there are more good products.