If I go down the reduce intensity of output route to something as dim looking as 15% am I okay to keep the CO2 high, or would I need to dial this back for any reason? Same question goes for ferts I suppose.
Hi Reuben,
CO2 and nutrients are the fuel used to make food. Ask yourself this question: Is it OK to have a full tank of petrol in the car even if the car will always be driven on "B" roads far below the speed limit?
Fundamentally, the reason we have plant problems is that we are driving the car on the motorway far
above the speed limit and we are running out of petrol.
When you have problems in your tank consider that the reason is that there is insufficient food caused by insufficient fuel with which to make that food. This is a fundamental principle that people seem to have difficulty grasping. Plants do not grow because of light. They grow because of food. The light is the oven used to make the food.
The higher the intensity of the light, the higher the temperature of the oven. In the car analogy, the higher the speed of the car. So when you have lots of light you are careening down the motorway out of control just like those police car chase real life videos. When you reduce the intensity then the car is being driven at a more controllable speed. You will arrive at your destination, but it will take longer and you are less likely to have a collision. If you reduce the temperature of the oven the food will take longer to cook, but there is less chance of burning the meal to a crisp.
If you can hold to these analogies then the solutions to the problems become so obvious. To cook the food, the oven requires some minimum temperature. Presently, you are far above that minimum temperature, the food is burning, smoke is billowing from the oven and yet you are worried that there may be problems if you lower the temperature of the oven. The joyrider in the stolen vehicle wonders what he needs to do to make the car go faster.
Seriously consider these analogies and it won't take long to understand the state of affairs in planted tanks. As an historical perspective, the planted tank scene really took off with the advent of CO2 injection. Conversely, people started having major troubles with the advent of T5 lighting which is brighter than T8.
Therefore, when we suffer health problems in our tanks the very first response should be to reduce the demand for nutrients/CO2 by reducing the light, and at the same time, to increase the availability of CO2/nutrients. This gives us the best chance of recuperation. We really never need to worry about the implications of lowered light intensity, because it was high intensity that got us into trouble in the first place.
Here is one of the major differences between higher plants and algae:
Algae require more light to survive than do higher plants. The reason? Simple. Plants have vast storage facilities. They collect CO2 and nutrients, make food and store the food in grain silos. Some of the food they eat of course, but as long as they make more food than they consume, the extra will always be stored for later hard times. The lower the intensity of the light, the slower the food is produced, but again, as long as the rate of food production exceeds the rate of food consumption there is never a problem.
On the other hand, algae don't really have an elaborate storage facility. Algae live in the here and now. They cannot depend on a food bank so when food runs out they starve. Their advantage though is that they are very small, very lean and don't have very complex systems which need to be fed. So, the higher the light the faster they can grow and reproduce. Since they are small they don't really need as much CO2 or nutrients. Think about how much of the diatoms you collect when you are cleaning the tank. Although it looks messy and they seem to be everywhere, when you collect all the algae in your hand and pull them out of the water there is actually not that much weight compared to say, a stem of Ludwigia. Algae are thousands of times smaller than plants and so require thousands of times
less nutrients and CO2 than plants do. That's why it's so crazy when people talk about how adding more nutrients causes algae. Algae really don't care how much CO2/nutrition is in the water. They only care about how much light there is. It is the plants that worry about having lager amounts of CO2/nutrition because they require lots of it, especially if the lighting is high.
So, within this context, think about a blackout. When you do a 3 or 4 day blackout, the plants are not too perturbed because they have stored large quantities of food, so they just carry on. But Algae quickly use up what little food reserves they have and then they starve because no light is available to produce food.
If you perform the blackout but then return to high lighting without fixing CO2/nutrients afterward, what happens? Algal spores bloom again and plants suffer again. But if you return to high CO2, high nutrition and low lighting, then the plants are not stressed, they make food, replenish their food reserves and carry on. The low light prevents the spores from blooming.
So, if you keep the lighting very low then it doesn't really matter how long the photoperiod is. The plants continue on in a slow pace until some weeks pass when they are strong and healthy enough to make physiological changes which enable them to adapt to higher light and to make better use of the higher light.
If you keep the same high intensity then the damage is still being done to the plants and diatoms are still loving it, so you have to guess or experiment with photoperiod length to determine how long it should be. I have absolutely no idea whether 5 hours of 50% intensity will be OK. No idea at all. I'm much more confident though that blackout plus 10%-15% will kick the diatoms in the groin. It's a certainty...
Cheers,