As mentioned by some other people, invasive algae are the result of a mix of nutrients availability plus the right conditions of light and CO2. In oceans, algae bloom happen when nutrients are available as non-limiting factors and the temperature and light increase from colder waters to warmer, which also helps the growth. The increment of light allows also the algae to proliferate faster, but the light is not really the cause of it, just an additional factor.
In freshwater, especially in closed pools like lakes are steady rivers, the algae bloom is related to the eutrophy, which is also spammed by a combination of excess of nutrients in non-limiting circumstances plus light and low levels of CO2.
Heavy planted plants are less likely to suffer algae because the consuming rate of nutrients is higher, so the water depletes faster than recovers them, which avoids the problem, so far CO2 levels are right so the plants can do the proper photosynthesis. Without the right levels of CO2, the plants lose efficiency so nutrients start to accumulate allowing the growth of algae.
Less hours of light works because algae are more dependent on light to survive than plants (in general). By cutting light to the tank, the algae cannot grow. However, it does not help at all if you do not solve the issue why they appear, which is the combination of light + nutrients.
Cleaning the tank and removing wastes helps because of the mentioned bacteria in this thread: If enough dissolved and particle organic matter exists in the tank, the natural cycling of matter done by bacteria will become it into nutrients that sum up to the fertilizers and soils, leading to the mentioned statement of non-limiting nutrients.
Reducing temperature also helps, because the dissolution of gases in water depends strongly on that, which helps to have better CO2 levels in the tank. It also affect to the speed of metabolism of plants and algae, and when the last ones are having some control in the tank, a reduction of a couple of degrees can help.
In summary, under my criteria, we can split between actual solution, palliative solutions and radical solutions:
Actual solutions:
1. Control of nutrient levels: Water changes and control of the dosage of fertilizers (as done in ADA system during the first two weeks, basically).
2. Balance the nutrient levels: Check what you are adding to the tank and frequency to see if your parameters are under control. Sometimes the problem comes from deficiencies in iron or trace elements respect to the concentration in the macronutrients, so the real point here is not the amount of nutrients but the proportions between them, and here there is no magic answers as strongly depends on the amounts and type of plants, as well as light spectrum and temperature or soil characteristics, so it can be achieved only via experience and behavior of each tank.
3. Improve CO2 levels: By adding more CO2 or adjusting kH, or both.If CO2 is not a limiting factor under light conditions, then plants can get maximum efficiency in productivity.
4. Clean-up of filter media and mechanical removal of wastes and damaged leaves, so heterotrophic and remineralizing bacteria cannot make the day for the algae.
Palliative solutions:
1. Reduce the photoperiod of your tank to avoid or reduce the algae population in the tank.
2. Mechanical removal of algae when possible.
3. Addition of species that eat the algae.
4. Adjustment of temperature to increment CO2 levels and reduce metabolism speed of the algae.
Radical solutions:
1. Blackout: Some people have succeed cutting off algae populations with a black-out for several days. This will harm also the plants, so it is not very helpful, as the algae will come back, and probably even worse than before, if you do not manage to solve the problem that caused them in first place. Spring blooms in ocean over polar areas can help to understand what happens when you turn off the light some days, the bacteria degrade the wastes increasing the nutrients, and you turn on later the light.
2. Glutaraldehyde dosage: Apart from the fact the product is really toxic and dangerous, it can be very harmful for your tank if you do not control properly the dosage.
3. H2O2 dosage: The same as above when goes to the tank's health. As mentioned also, H2O2 will help to attack punctual spots of algae. It is bad idea to provide this to the tank as "normal" solution to prevent algae.
4. Rest the tanks: Which only will work if you learnt something about what caused the problem in the tank, so you do not make the same mistakes.
In general, the only way to really avoid algae pass by the actual solutions; palliative solutions are OK when you already have it and as a first approach to the problem; radical solutions should be only applied when all the other methods did not work or the algae already damaged your plants at such a level that you can risk them.
Of course, this is just my opinion about this topic, and there will be many specific cases requiring something else, or specific algae coming for different reasons.
