Name that Buffer!

[JDogg]

ok i am putting this in the planted forum because it deals with a planted tank... if this is the wrong place then feel free to move it, just let me know where you put it

Stats
10 gallon planted tank
Eco-Compleat Substrate
Dosing KNO3, KSO4, KH2PO4 and CSM+B by to the EI method
Ceramic Cave, Ceramic Easter Island Head Cave, Terra Cotta Cave decorations
DIY CO2
Fist Size ball of Pat Moss in the Filter (know it is doing something cause water has slight yellow color...

List of Plants
Stargrass: Heteranthera zosterifolia
1 Amazon Sword: Echinodorus amazonicus
1 Ozelot Sword: Echinodorus x. 'Ozelot'
2 Oriental Sword Echinodorus macrophyllus
Limnophila aquatica
Hygrophila polysperma v. Sunset

List of Animals
Pair Apistogramma nijsseni
6 Neon Tetra: Paracheirodon innesi
2 Oto: Otocinclus mariae
Malaysian Trumpet Snails

Water From the Tap
PH= 8.0
KH= 13 degrees
GH = 21 degrees

After 1 50% PWC and 3 25% PWC using only RO water!
PH=~7.4
KH = 6 degrees
GH = 9 degrees

those just do not add up in my to me, what could be buffering the water?

now the RO is from the grocery store (re-fillable gallon jugs) so i am assuming there machine is working...it test 0 KH/GH and 7.0 PH just as would be expected

Picture of the tank

[maxwell1295]

Maybe the rocks?

[JDogg]

Originally Posted by maxwell1295

Maybe the rocks?

the ceramic caves..that is possible, but assumed since they are manufactured for aquarium use they should be inert... but it is possible

[Zezmo]

The numbers to not actually seem that out of whack. Perhaps also consider test variance.
If you suspect somethingis adding buffer, then...without water changes, the Kh should slowly rise over time.
Place the suspect item - cave, gravel, rock etc in a bucket of pure RO/DI or Distilled water and see if that raises the Kh. RO water should not have a Ph of 7 btw, but a Ph of 6 or less, the readings from the store water are already suspect from that alone.

[JDogg]

Originally Posted by Zezmo

The numbers to not actually seem that out of whack. Perhaps also consider test variance.
If you suspect somethingis adding buffer, then...without water changes, the Kh should slowly rise over time.
Place the suspect item - cave, gravel, rock etc in a bucket of pure RO/DI or Distilled water and see if that raises the Kh. RO water should not have a Ph of 7 btw, but a Ph of 6 or less, the readings from the store water are already suspect from that alone.

you are going to have to explain that last statment, why would RO have a PH of 6 or less? pure water is 7.0 that is why 7.0 is neutral on the PH scale.

so you are saying the RO process actualy should be adding free H+ ions to the water??? turning it into a week acid?

[theotheragentm]

Where did you get the Easter Island head? That's so cool.

[JDogg]

Originally Posted by theotheragentm

Where did you get the Easter Island head? That's so cool.

LFS

[Zezmo]

Pure RO/DI water does have a true Ph of 7.0. Although, when exposed to atmosphere it should drop to about 5.5-6.0 due to absorbed atmospheric CO2, and the lack of buffers in the water. This is not true Ph drop, but the acidic effect of CO2. If using any common hobby grade Ph tester the resultant Ph should be in the acidic range for any ultra pure water. Unless the atmospheric CO2 is somehow purged.

[JDogg]

Originally Posted by Zezmo

Pure RO/DI water does have a true Ph of 7.0. Although, when exposed to atmosphere it should drop to about 5.5-6.0 due to absorbed atmospheric CO2, and the lack of buffers in the water. This is not true Ph drop, but the acidic effect of CO2. If using any common hobby grade Ph tester the resultant Ph should be in the acidic range for any ultra pure water. Unless the atmospheric CO2 is somehow purged.

ok that makes sence

well the RO i tested was in a bottle with a tight cap, i do not think there was mcu time of atmospheric CO2 to get into it...