More aeration higher PH?

[Memphis118]

I recently purchased a new 17 gallon tank because my old 30 gallon was leaking. I went and  got everything brand new and started from scratch (using old plants / drift wood) for the instant cycle. 

 

I am currently using Mr. Aqua plant soil, which buffers my PH down to 6.1-6.2 (guarantees 6.0-6.5). I have been using the DO!Aqua poppy glass intake, and it does not cause much ripple for o2 exchange, so I decided to use an Airstone.

 

Turning on the airstone, my PH starts to rise from 6.1 to about 6.6 / 6.7. If I turn off the airstone, it will slowly drop back down to 6.1. Is this normal? I am not running any co2 in this tank, so there shouldnt be too much to gas out.

 

Current Parameters:

 

PH 6.1 (without airstone) 6.6/6.7 (with airstone)

GH 5

KH 0-1

Nitrate >10ppm

Nitrite 0

Ammonia 0

 

I also have 1 amano shrimp, and 4 otos for algae cleaning

 

Thanks

[chibikaie]

I hope you mean less than 10 ppm NO3-, as greater than 10 ppm is a kind of meaningless value. < is less than.

I tried doing some searching, but can only come up with off-gassing excess carbon dioxide. My only guess is that the buffering capability of the soil involves the bicarbonate buffer system in some way, and this is somehow generating enough CO2 to lower the pH to the values you are seeing unless driven off using the airstone.

[Memphis118]

I hope you mean less than 10 ppm NO3-, as greater than 10 ppm is a kind of meaningless value. < is less than.

I tried doing some searching, but can only come up with off-gassing excess carbon dioxide. My only guess is that the buffering capability of the soil involves the bicarbonate buffer system in some way, and this is somehow generating enough CO2 to lower the pH to the values you are seeing unless driven off using the airstone.

 

Sorry, less than 10 ppm Nitrate. 

 

The soil I am using is http://www.amazon.com/Mr-Aqua-Water-Plant-Aquarium/dp/B007BJ21MI

 

and I havent read anything about it that would have any kind of co2 that would be buffering the PH down. Currently it's at 6.67, which isnt bad for CRS, but I am just not exactly sure why shutting off the airstone, will give me 6.1-6.2.

 

I also searched around online, with no luck. 

 

 

On another note, if I decided to leave the airstone off, my tank will have little to no surface break. Would that effect the shrimp in any kind of way?

[chibikaie]

The consensus among plant folks seems to be that there should be good water movement from the lily pipes, not necessarily breaking the surface with bubbles, and this should allow enough oxygen exchange for the fish while not driving off injected carbon dioxide. In theory, this would be plenty for shrimp as well, given that they are smaller, but I'm not sure if that is a safe assumption.

Unfortunately, I don't know how each buffering soil works. The primary buffer involves bicarb, which can turn into carbon dioxide - especially if the extra off-gassing from the airstone is driving off CO2 as it is formed. It would encourage the reaction to keep going in that direction.