Qoute : Tom Barr aka PlantBrain
""Why water change day seems to grow aquatic plants better
Basic simple question: why do my plants seem to grow better/best the day of the water change?
I do a large water change in the morning right after the lights come on, then late in the day, there is mad pearling and obviously better growth than any other day of the week.
I've measured plant growth to confirm this also. (stem length and biomass).
I've also done back to back water changes over the entire week, once a day, same time.
I've suggest a few hypothesis:
1. CO2 rich tap water. This is supported and suggested in the Optimum Aquarium(1986) from Dupla's Horst and Kipper, often around 20-30ppm ranges.
One can/could test this by allowing the water to sit for a 1-2 days to degas, then change the water.
Results, we still see an increase in growth.......but this is inconclusive.
I agree there is some strong effect here.
2. Temp differences within a sealed hot water heater and cooler tap water degas once released into the aquarium= cool water holds more gas, O2 and CO2 etc. Same issue as above, plenty of gases available to help growth. Test similar and similar results to above #1 as well.
3. Exposure to air. Plant aerenchyma (think a sponge in water and squeezed, and then out of water and squeezed) acts like a sponge and takes up lots of gas/air and then uses that while exposured during the water change. Larger water changes seem to produce this effect.
Test: large water changes by continuous drain and fill methods vs big drain and then refill after exposure. Seems to be plausible. Results suggest the same. You still need to allow and account for the degassing of the tap water also.
4. Indirect O2 addition= > drives bacterial cycling much faster= . indirect impact on plant growth.
5. Gas films. This was discussed by Ole in TAG, vol 23, No#1, pgs 32-39
A physical gill that improves submersed O2/CO2 exchange in some wetland species. If you add enough CO2, then the gas films do not have any difference in growth rates with/without the gas films(see Fig 7). This is similar to exposing the plants to air during the water change.
i thought i'd add to this and share here, that my water degasses for a whole day now in a big garbage can. water is brought to close to room temperature and i replace 80% of the water in my sump and in my tank.
water is 76 degrees going in, tank is kept at 78/79
there is no extra oxygen as i jsut have a small pump in the garbage can.
water change is done without lights or co2 on but after the water change is done, plants look "better" i think we can all agree to this, no nutrients added, no co2, no lights, but my plants look awesome.
everything is turned on, lights hit and boom bubbles bubbles everywhere.
there is no saturated water for this to be fake pearling. and don't get me wrong my tank is a sodapop tank every day, but this is just madness
its a stupid hypothesis, but i think plants just like clean water too