[Optix]

1. fix nutrients
EI so youre good

2. control CO2

if youre low on CO2, thats your limiting factor...either up CO2 or lower your lighting

3. enjoy your tank


the simplified answer to your question is...when a plant depletes whatever nutrient (CO2, nitrogen, calcium, potassium etc), complete/proper/ideal photosynthesis stops ...and you get deformed plants

so if you had A LOT of CO2 and no nitrogen, the plant shuts down...giving algae a chance to move in
but if you keep the plant happy (with nutrients in excess, and light in moderation)...the plant will be photosynthesizing until the lights turn off (never giving algae a chance to take over, though it is always there)

it took me a while to [STRIKE]understand[/STRIKE] accept this point

but it really is that simple

 

[Optix]

yes, that is incorrect

Light is the gas pedal -controls the speed of growth in the plants

Nutrients are the fuel -without fuel, your car wont move regardless how hard you hit the gas pedal

CO2 are the tires -if you have a flat tire (insufficent CO2), you can only drive so fast safely (adjust light intensity depending on pressurized CO2/DIY CO2)