There's a balance. Plants can only do as well as the lowest available resource. When that's exhausted, the plant shuts down and stops the uptake of nutrients and the rest of the resources sit in excess for algae to capitalize on since they aren't as advanced as far as processes.
Plants have photosynthesis and respiration, light on photosynthesis ( light,
co2, nutrients = creation of glucose for energy production of oxygen), lights off respiration (those created sugars + oxygen, creation of co2 that's released, the plant working 24/7.
Now if you run short on something, the plant can't perform these functions well, or at all if something is depleted. This leaves excesses in one or another area for algae to capitalize on.
If you run excess nutrients you'll get algae also. Excess light also algae, excess co2 also excess algae.
So where does this leave us?
Too much co2? Do you add co2? If not it's unlikely the plants are creating too much alone, but too little? Also unlikely if you have low demand plants and not heavily planted.
Too much light? Recommendation is 8-10 hours generally, however in a new tank with small plants it might be as low as 6 hours a day, so there isn't excess light for algae.
Too much nutrients or a deficency? If you are using a fertilizer, this is usually the problem and it's usually too much, far more than your plants can use. Heavy and very regular
water changes can remove them, more plants, can remove them.
A deficiency might occur if you are heavily planted.
, think of the aquarium like a potted plant. One plant in the pot you might fertilize 1x per year. 20 plants in a pot you might need to fertilize 1x per month, 50 plants in a pot you might need to fertilize 1x per week. Theres still limitations to the pot or the aquarium though, you don't want roots twisting around each other and choking off plants, getting matted and root bound, but small volume of soil to hold nutrients and too many plants makes it run short, and too much fertilizers create excesses that are no good either, you'll get weeds, unintended plants popping up (like algae, the aquariums "weeds" also) to take up the excesses and can oitcompete the plants if allowed to run amok.
But there is a balance. Most people adjust and tweak until they get the results they were looking for. Reducing lighting, adding co2, adding more plants, doing more water change if they think nutrients are too high, adding or withholding fertilizers.
There are nutrient testing kits, meters and monitors also, if you wanted to approach it from a scientific angle and know the numbers,
Your cause is most likely too much fertilizers for the plants you have. Excess that causes algae, algae that coats plants and interferes with photo synthesis, and your water changing schedule should be 1x per week, or more, until it's controlled and the excesses are taken down. You should be fertilizing just for what the plants need, the extras just feed the nuisances, too much of a good thing like fertilizer is a bad thing, if the plants get Coated and can't take the light efficiently, they can't take up nutrients efficiently either and convert them to sugars to grow.
So add more plants, reduce fertilization, increase water changes, and play with this until you find the right balance, or buy the monitors and tests and see where the nutrient problem is exactly.
Most folks change it up until they find what works.
)
