I have a reef tank, and would like to hear how you guys prevent algae in planted tanks. In the reefing world, the strategy is nutrient reduction. Is this what you do in planted tanks? Do you leave some nutrients detectable in the water? Will algae not grow with small amounts of nitrate and phosphate?
Interesting that a reefer is asking for the planted tank perspective on things. Personally I often look to reefers for philosophy and inspiration!
The core strategy is to keep a large number of plants growing well at all costs. Plants will keep the water clean, taking up all the nutrients algae need to grow. It's also possible they emit chemicals inhibiting algae, though this topic is not well-studied. Meanwhile healthy plants leak organic matter/nutrients, which feeds algae (this is why algae oftentimes grows on older leaves in poorer condition).
Nutrient reduction is a strategy, to a degree. There is one popular method, Estimative Index (EI), that absolutely loads the water with nutrients to ensure no deficiencies. But this is not good for running a stable tank. Leave the tank alone for a few days, or have a minor accident (like a dead fish, or CO2 running out), and the cleanup will be backbreaking. Not to mention the risk of toxicity (to both plants and fauna). I have found leaner methods, like ADA, works better. Dose just enough to meet the plants' needs, and no more. For me this means I dose until there are no more signs of deficiency. For macronutrients I find maintaining 5 ppm NO3 and 1 ppm PO4 is a good sweet spot, giving enough buffer for the plants while not being enough to encourage algae growth. This is for my CO2-supplemented tank filled with fast-growing stem plants; if I had just slower growers like ferns or Cryptocoryne I could probably get away with even less.
Of course the other things like light, CO2, are important for keeping plants healthy. But there is one subject that is often ignored: microbial balance.
There are more microbes in our tank than those involved in the nitrogen cycle. They serve a myriad of essential functions, including processing various organic wastes and making nutrients accessible to plants. Of course, there can be bad ones as well. When microbial balance is tipped away from the beneficial kinds, algae often results. Conversely promoting good microbial balance will combat algae. For example, using a product like ADA bacter balls in a spot with BGA will literally lead to the BGA receding/disappearing within days.
How does one promote a healthy microbial population? Sufficient filtration capacity is a big one. However substrate choice and oxygenation are also very important. Soil substrates, in addition to providing nutrients for plants, are also excellent for supporting the microbial population, especially when combined with a lower layer of volcanic rock (like lava rock pebbles). Maintaining adequate oxygenation is also essential. Make the sure the surface is clean (no oil slick film preventing gas exchange), and aerate the tank at night.
Lastly, the tank's first month or so can make or break it in terms of stability and algae issues. This is a
very good link discussing the topics I mentioned in this post, as well as going over best practices for starting a new tank. It is a long read but worth every bit. You will learn more in an hour of reading this than a whole week of reading random forum threads.
