PH Question

[roadkingray]

I have a 75 gallon tank that has a ph of 6.5. My question is if the R.O. water I am using has a ph 6.0. Should i use a buffer to bring it closer to 6.5? The tank has baby black aros in it and I am aware of how delicate they can be.
Thanks, Ray

 

[Toby_H]

If you plan to do 50%+ water changes then it would be a good idea... but if you are doing typical 25% water changes then I would not.

Keep in mind the PH chart increases/decreases exponentially from the starting point of 7...So the drop from 6.5 to 6.0 is much smaller than the drop from 6.0 to 5.5

Also remember a stable PH is more important than a specific target number. So if you do choose to add a buffer I suggest adding it to the refill water before you add that water to the tank. Adding water with a lower PH, then adding buffers, can cause fluctuations that the fish will not appreciate.

 

[roadkingray]

Thank You!

 

[squint]

Keep in mind the PH chart increases/decreases exponentially from the starting point of 7...So the drop from 6.5 to 6.0 is much smaller than the drop from 6.0 to 5.5

The pH scale is logarithmic, not exponential.

pH 7.0 = [H+] of 1x10^-7 M
pH 6.5= [H+] of 3.162x10^-7 M
pH 6.0= [H+] of 1x10^-6 M
pH 5.5= [H+] of 3.162x10^-6 M

A drop of 0.5 from 6.5 to 6.0 represents a 3.162-fold increase in H+ concentration. Likewise, a drop from 6.0 to 5.5 represents a 3.162-fold increase in H+ concentration.

Also remember a stable PH is more important than a specific target number.

So if you do choose to add a buffer I suggest adding it to the refill water before you add that water to the tank.

If you added an alkaline buffer to the replacement water, you would still have to add the replacement water slowly since it would likely affect the pH of the tank water.

Adding water with a lower PH, then adding buffers, can cause fluctuations that the fish will not appreciate.

It's the magnitude and rate of qualitative changes of the water, not frequency, that one is trying to avoid.

Lastly, osmotic shock is probably a much bigger danger than changes in pH. The solution is the same though.

 

[boldtogether]

If you know were these fish came from you could inquire into the breeders ph. If it is a local breeder, chances are very good you share the same water source, therfore, ph should stay at what they have been raised in.
Just my 2¢.

 

[Toby_H]

I love science

The pH scale is logarithmic, not exponential.

You are correct, it is logarithmic... but a logarithmic scale is often exponential...

pH 7.0 = [H+] of 1x10^-7 M
pH 6.5= [H+] of 3.162x10^-7 M
pH 6.0= [H+] of 1x10^-6 M
pH 5.5= [H+] of 3.162x10^-6 M

The ^-7 means to the negative seventh power...
Multiplying 3.162 by itself an increasing amount of times makes it a larger difference each time the ^# increases...

Thus I repeat, the change between 5.5 to 6.0 is much larger than the change from 6.5 to 7.0

A drop of 0.5 from 6.5 to 6.0 represents a 3.162-fold increase in H+ concentration. Likewise, a drop from 6.0 to 5.5 represents a 3.162-fold increase in H+ concentration.

You forgot to factor in the ^#...

If you added an alkaline buffer to the replacement water, you would still have to add the replacement water slowly since it would likely affect the pH of the tank water.

If the tank water is buffered to 8.0... and the tap water unbuffered is 6.0...
Then buffering the tap water to 8.0 prior to adding it to the tank which is at 8.0 will allow you to add it at a fast rate...

It is likely that over the course of time the buffering capacity will get "eaten up" (meaning countered by acids being produced within the environment)...

Often hobbyists will use baking soda (or similar) to buffer the PH to the desired tank PH... as well as put a small portion of crushed coral in the fitler to help maintain that desired PH.

It's the magnitude and rate of qualitative changes of the water, not frequency, that one is trying to avoid.

Lastly, osmotic shock is probably a much bigger danger than changes in pH. The solution is the same though.

 

[squint]

You are correct, it is logarithmic... but a logarithmic scale is often exponential...

No, logarithmic functions and exponential functions are the inverse of one another.

You forgot to factor in the ^#...

Nope, 1x10^-6 / 3.162x10^-7 = 3.162 and 3.162x10^-6 / 1x10^-6 is also 3.162.

If the tank water is buffered to 8.0... and the tap water unbuffered is 6.0...
Then buffering the tap water to 8.0 prior to adding it to the tank which is at 8.0 will allow you to add it at a fast rate...

The real danger is osmotic shock. People who know more about chemistry than I do (I only have a minor in chemistry) tell me that pH shock basically doesn't exist and that osmotic shock is what we should be concerned with. So while the pH of the tank and replacement water might be the same, it's prudent to make sure the TDS match if you want to replace the water quickly. Or you could just do it slowly and not worry.