adli100 said:
i understand that plants need co2 but am sure i seen plants in tanks where there was no co2
No...you didn't. This was self hypnosis. You saw a tank that had ambient CO2 levels like yours but was not bombarded with as much light as yours. You need to understand the relationship between light and CO2. It's fundamental and it goes something like this:
1. Light is converted by the plant into electricity. More light means more electricity.
2. This electricity is then used to run a conveyor belt and to power a reaction that turns CO2+nutrients into a sugar. More electricity speeds up the conveyor belt and grabs more CO2+nutrients from the environment to power more reactions and thus produces more sugar.
3. The sugar is used to feed the plant and to make it grow. More reactions means more sugar. More sugar means more growth.
Now, put on your thinking cap and work your way backwards. What issue do you have? No growth, right? =>Please see step number 3. It means no sugar production, right?
How could that happen? => Please see step number 2. You have lots of power, a fast conveyor belt and no ingredients to make sugar. What do you think happens to your powerplant? Was your answer "complete meltdown"? If so then you're on the path to wisdom.
So how can this be fixed?
How about slowing down the conveyor belt to a speed that can accommodate the available level of CO2+nutrients? You need to either lower the light intensity or to add more CO2.
In the non-enriched tank that you observed, the amount of light being thrown at that tank would have been low enough to avoid overspeeding the conveyor belt. The CO2 was being pulled from the atmosphere. As the plant absorbs CO2 from the water more dissolves into it from above. At low ambient levels of CO2 the plant becomes more efficient at collecting CO2, but this is disrupted if you are constantly firing Klingon Photon Torpedoes at them. The deeper the tank the more difficult it is to get dissolved CO2 all the way down to the recesses.
Look for ways to stop torturing your plants. Do you have reflectors? Get rid of them for now. Shut down the two 18 watt tubes. Keep your photoperiod less than 8 hours for now. Lower the temperature. This lowers the metabolism of everything in the tank - plants AND algae, and it gives you room to breathe. If you decided against adding liquid carbon then avoid water changes. This helps the plant to perform the adaptation to low CO2 and to become more efficient. If you decide to add liquid carbon then ensure that you add it every day.
Were you dosing NPK as well as trace elements? If you decided against liquid carbon you don't really need a whole lot but you do need to add some.
What type of algae do you have? You need to identify the algal species because it will tell you what it is that you are missing. Please carefully review
JamesC's Algae Guide compare the images and report back as to what species are in your tank (in fact the guide tells you what the causal factors are.)
Cheers,