All my levels are low and I change 8 gallons of water every two weeks. Secondly, I get algae, looks like hair, growing on the substrate on the bottom and some of the dead corals. This algae seems to grow like mad for 2-3 weeks then die off. Then it starts again 1-2 months later. I will assume you are talking about the coralline algae.
Coralline algae rely on a number of factors to grow well.
Number one is water chemistry, specifically calcium, alkalinity and pH. Since you did not provide me with any of this information I can only speculate as to what may be happening. Unless coralline algae have sufficient calcium, bicarbonates and carbonates in the system to calcify they will not do well. Other factors include high phosphates that impede the calcification process in coralline algae. Phosphates should be lower than 0.2 ppm. Strontium chloride additions also appear beneficial for coralline algae growth.