This week we began by discussing and assessing our plant growth. It had been 3 days since the introduction of injected CO2 in our tank and it has made a noticeable difference to growth! It is now possible to view photosynthesis in action! As the plants release oxygen from the underside of their leaves bubbles collect under the leaves and can sometimes be seen streaming out and rushing to the surface of the water. All of our stem plants are showing signs of new growth. Most visible growth can be seen with the star grass, Heteranthera zosterifolia. The new growth on the Rotalla wallachii is red suggesting that the light intensity/spectrum that we are providing is more than adequate.
We discussed photosynthesis and time cycles. We talked about the ideal time for the co2 injection to begin and end. We decided that injecting an hour before lights turned on and stopping the co2 input an hour before lights-off would be ideal. This would allow adequate supplies of CO2 to dissolve in the lead up to lights so that photosynthesis could be maximised. Turning off the co2 before lights off would allow the excess co2 to be used for photosynthesis and prevent excessive amounts from building up – this can be lethal to aquatica fauna.
We then moved onto discussing the algae which we have also seen an increase in. It is a rather unsightly nuisance and we talked about the dangers of an algae bloom. Mr Short shared insights into how algae build-up can lead to the destruction of our tank – death of plants/animals – as vital O2 is sucked from the water column.
We talked about strategies to manage the algae, including removing it by hand, as well as the delicate balance of lighting/nutrients/co2 and using fish/shrimp to control algae. This also led into discussions about ecosystems/food webs/chains. Adding too many algae eaters could become problematic as once they have eaten the majority of the algae, there would not be enough to sustain their population.
Pupils went away with a research task of consider which species of animals we should stock as well as how many.
We look forward to gathering their ideas next week before heading out to stock up.