I am not a plant or algae expert, nor am I a biological science person...but I think this is VERY BASICALLY how it all works:
AFAIK, algae will grow (well) if the tank has an abundance of any one (or more) of the following:
Nitrate, Phosphate, CO2, or light.
Plants compete with algae for these nutrients and usually win. A plant flourishes when micronutrients (iron and other nutrients), macronutrients (nitrate, phosphate, potassium), and C02 are available for use. Then, based on the amount of light available, they will use A amount of nitrate, B amount of potassium, C amount of ... etc., where A, B, C, etc are rates of consumption. (this is all greatly simplified and probably mostly wrong)
Now, lets assume your tank has an appropriate level of phosphates, an appropriate level of potassium, an appropriate amount of light, etc, but a high level of nitrates. The plant would like to use all of the nitrate, but the lack of light and other nutrients limit its nitrate intake. It can only take what it wants and nothing more.
This is where algae steps in--it can take advantage of the fact that the plants can't use up one or more of the nutrients. The algae is fairly primitive and can't compete with a plant for nurtients. If the plant is using all that it can, then the algae can use up the excess (unlike plants, algae doesn't have such strict nutrient requirements--usually all it requires is one nutrient in excess and some light).
So, the trick to reducing algae (you'll never fully erradicate it) is finding the right balance of nutrients and light for your tank. Best way to do this is to stock up your tank with fast growing plants and then add nitrates, phosphates, and potassium to the tank in moderate doses. Then, measure phosphate and nitrate levels in the tank and monitor the nitrate and phosphate levels over a few days. By doing so, you can effectively calculate how much of each of the macronutrients your plants have used over X days.
This will allow you to fertilize appropriately for your tank and keep algae at bay.
For newt tanks, I doubt CO2 is added and I bet most lights are not the plant-grow varieties. This being the case, it might be difficult to balance the nutrients and adding fertilizers wouldn't be recommended. The only practical thing to do is reduce lighting and make water changes more frequently.
Good luck...and hopefully all that I said isn't a load of poopoo.
^iMp^