Pressurized CO2, Water changes and pH swings

Question:

Pressurized CO2 alters your pH. (I think it lowers it??) We all in agreement that if a fish is in a stable pH it will be fine, or ok. (Obviously the more finicky fish like Discus will be better in the proper pH).

When you do a water change, you remove CO2 saturated water... or rather water that has an altered pH. You then top up with tap or aged water that has a different pH. Is this not dangerous for the fish? Is there a limit to how big a waterchange you can do? Or am I reading into this too much?

Regards

 

yes it is dangerous.. ive done this before.. killed 70% of my fish i do a 50% water change MAX nowadays.. also with each bucket i fill i check to see if the fish are still ok

 

yes it lowers ur ph.. thats why ppl in ct with softer water have to use ph up so they dont get ph crashes

 

Ok... so I should only do a 50% W/C when absolutely necessary, but rather stick to a 20-30% weekly?

 

ya.. i'd say 30% is enough.. but if u religiously do water changes weekly 50% should be fine.. if u start to notice strange behaviour in your fish (coming to surface to breath or swimming irratically) during water changes, STOP imidiately.. wait a day and fill the rest of the tank..

also, dosing CO2 you have to add much more ferts as plants take them up at a monstrous rate.. common problem is a potassium def.

 

Ho
I've got too much potassium in my tank.Not adding any.Only from rotting plant leave i suspect.

 

You mean Phosphates. K/Potassium deficiency results in pinholing

 

Ditto:embarrest:

 

@Zoom,
You can confirm the following with the Prof.
In a planted tank,without Co2 injection, the combination of continual respiration,from fish,and photosynthesis,from plants during daylight,creates a fluctuation throughout the day that affects oxygen and Co2 levels.
Rising and falling O2 and Co2 levels has a direct affect on ph and water hardness.This is called diurnal fluctuations and occurs in all natural waters.
So during the day,in a planted tank,your ph will rise because the plants are using the Co2 faster than the fish can produce it and carbonic acid production also falls.When all the Co2 is used up,the plants start using bicarbonates as a source of carbon.This causes the water to become softer.With high ph and soft water you have pretty unstable conditions.

At night,plants stop photosynthesizing and stop producing O2,but don't stop respiring.This Co2 production coupled with fish respiration,reduces O2 in the tank.The Co2 will bind with minerals,creating bicarbonates,and with organics,creating carbonic acid.These processes raises alkalinity,bicarbs,and lowers ph,carbonic acid.So at night your ph falls and your alkalinity rises.Again pretty unstable.

By injecting Co2 at a constant rate during the day,we can control and reduce these fluctuations.The plants uses only the Co2 and not the bicarbonates.
Ph will still fluctuate because of the difference in O2 and Co2 levels,but your fish should be used to this.It is more important to keep the carbonate hardness,buffering,stable.A lack of buffering capacity will cause greater fluctuations in ph levels.

That's why they guys in the W.Cape,our soft water, have so much trouble when keeping plants and fish together.