Tonser said:
Morning all, and thanks for the replies guys.
ceg4048 said:
What you might be able to do to get some idea this is to add Excel at water change time to compensate in part for the CO2 drop off.
I didn't have the energy to trawl though all 16 pages but lighting might be a factor here as well. I know at least a few of you guys to be sneaky Klingons. Are you using advanced thermonuclear gamma ray photon weapon technology above the tank (as some are wont to do)?
Hi Clive, the lighting is 2 x 54w T5HO tubes from 10am to 4pm daily. I'm still wondering what is the best time to do the water change though ?
From the above posts, if I do it too soon after lights off, the plants wont like the sudden CO2 drop (its only a 15% wc), but if I do it too close to lights on, the CO2 level will be low when lights come on. This is why I have it at midnight as I thought it was a good balance between the 2.
Tony
Hi Tony,
Well that lighting seems pretty reasonable to me mate. JamesM had mentioned to me that he saw an improvement in one or two of his tanks when he altered his water change schedule. This led him to the conclusion that the time of day was a contributing factor. The problem is that he had also made several other changes over the period of a few weeks along with an adjustment to the change schedule. So it's difficult to draw any conclusions about a particular variable when other variables are not held constant. Additionally, some responses to environmental changes are either not linear (i.e the change in output is not proportional to the change in input) or occur over time - for example you can do something today and not see the results that are directly related to what you did for a week or more.
So really, although I'm not doubting James' observations, I guess I'm not convinced that the time of day for WC should play a significant role.
Photosynthesis is divided into two major sub-systems called Photosystem I and Photosystem II.
Photosystem II occurs first and is light dependent. In this phase, light strikes the chlorophyll which starts a chain of events that splits water and liberates Oxygen (pearling lives here). The ionized Hydrogen is use to power a factory that produces a stored energy compound called ATP (Adinosine Triphosphate - PO4 haters please take note!).
Photosystem I is called the Calvin Cycle which requires a lot of energy. It uses the stored energy of the ATP to "fix carbon" from CO2 and to use the Carbon to build a phosphate sugar called 3GP.
For a long time, it was believed that Photosystem I doesn't require light, so I think that might be why the idea that CO2 is used in the dark may have arisen (and in a way that's not far from the truth). The thing is that if there is no light then there is no ATP production from Photosystem II (which
is light dependent) and so Calvin Cycle grinds to a halt.
The enzyme Rubisco lives here. Remember Jason Stratham as The Transporter? Well Rubisco is The Transporter of CO2. The amount of Rubisco is finely tuned to the amount of CO2 that the plant senses, but because Rubisco is a huge, complicated molecule, it takes days or even weeks to produce proper quantities. So if the plant senses, say, 30ppm CO2, it tries to produce enough Rubisco to Transport 30ppm of CO2 to the Calvin Cycle reaction chambers. If you then reduce the CO2 level to 20ppm then the plant has just wasted it's time and energy, now has to reduce the Rubisco levels, and the system starts to sputter. This is where BBA is triggered.
So if CO2 levels are stable, the Rubisco production/content is also stable (even if the CO2 level is low and stable - as long as the lighting is not too high).
When you do a water change on a CO2 injected tank, the transient CO2 level is so short lived that it does not trigger a response in the plant to revise the Rubisco production because on average, the sensed CO2 level is stable. The plant just carries on.
A continuously modulating CO2 level is a different story, so as Tom mentioned, the quality or performance of your equipment may be suspect. Imagine a needle valve or regulator that does not deliver a constant gas flow (or even an undetected modulating solenoid). A slow modulating gas delivery period could actually approximate the instability of a pH controller - remember those debates? Do you run your CO2 bottle down to empty? The cylinder valve's delivery may perform poorly at low content levels. That's why I prefer larger CO2 cylinders - more time at stable gas delivery performance before the CO2 content bottoms out.
These are just things to think about. I'm not saying these are certainties, just that we would be seeing a heck of a lot more BBA if it were dependent on what time of day we do a water change. You know me mate, I'm a lunatic and I've done water changes at all times of the day, 2 or 3 time a week even - and we're talking massive changes, you know the ones where the fish are on their sides flapping about? And I've not seen this phenomenon, so I reckon that if the water change timing is a factor, then it must be in combination with some other factor or factors.
Cheers,
I got in to that mess when designing with an American client who kept me up all night working. I found it much easier to do w/c after lights off at around 1 or 2am, but it just went from bad to worse. Going back to 10am w/c's really helped.
