What helps algae to grow? Ill tell you. First you need to know theese:
Phosphate, ammonia, nitrite, nitrates, silicate and iron. And light to fuel the chemical reaction so they can convert some of theese into food(sugar). Theese are the main things that all photosythetic organisms use. Reducing those to as close to zero as possible will slow their growth because there is less food available. Eventually they will die off. Much like a fish thats not fed, soon it starts to get sick, eventually it dies. Mostly if you remove 1 of theese 3, phosphates,silicates, nitrates they will stop growing. But if you remove silicate you wont get diatoms because they feed on it. If you remove phosphate, you will see less green type of algaes and reds. If you remove nitrate completely you will not see any algae, except maybee cyano. Wich can make its own nitrate from N2 gas dissolved in the water.
Where do phosphates come from? Well there are many sources. Mostly they come from organics that are not being removed by mechanical filters. Like how a skimmer removes the organics.By removing the organics you also export the phosphates with them. As well as nitrogen. Nitrogen leads to ammonia, nitrite and nitrates when the anerobic bacterial cycle takes place. Even phosphates that are bound to rock, can leach out and cause algae even though there is not any measureable phosphtaes in the water the algae are eating it as it comes out.
Sandbeds also can release phosphates if overburden with organics. The organics(dirt, fish poo, uneaten food) stuck under and on top of the bed will be a food source for bacteria. When one bacteria eats it it releases the phophates. Another eats it and releases nitrates. You get the idea.
Basically its all about removing(exporting) those organic particles. They are everywhere in your tank and its up to you to get them out. Trapped in the pore of live rock. Sitting on top of the sand, or under it. Leaving a mechanical foam sponge in the water.Dont remove organics and mother nature kicks in and algae grows and removes the left overs of rotting organics.The result is alot of algae.
Good luck
