Lowering PH question?

[jdrebit]

I am trying a heavily planted tank for the first time and I’m having trouble lowering my PH. Without adding anything my water parameters are:

Ammonia: 0
Nitrite: 0
Nitrate: 5-10 (just before weekly 25% water change)
dGH: 5
dKH: 3
PH: 7.5

I have started using a 2L DIY CO2 bottle with a power diffuser from a Red Sea Turbo CO2 system. I use Seachem’s Flourish, Trace, Potassium and Excel products per the dosing schedule. My substrate is 1 ½ bags of Flourite and I do have a nice size piece of driftwood in the tank (been submerged for over a year).

When I used the Alkaline/Acid buffers in the 2 to 1 ratio, I was able to raise the dKH to 7 keeping the PH at 7.5. Then I added ¼ tsp per day of just the Acid buffer to try to lower the PH. I can get it down to 7.2 (dKH drops to 5), but by the next day it’s right back up to 7.5. I have tried taking the PH reading at different times of the day, but it always reads 7.5. I have tried two different test kits and borrowed a digital PH meter, still 7.5.

When I did my last water change (4 gals) I added ½ tsp of Acid and ¼ tsp of Alkaline buffers to try and keep the balance, but again after a day my PH returns to 7.5.

Any suggestions?

[jdrebit]

Forgot my lighting is 48w T-5 HO, 1 plant grow bulb and 1 freshwater slimpaq 6700 degreeK bulb.

[Tech Support LK]

What CO2 level are you keeping?

[jdrebit]

Other than using a PH/KH/CO2 chart I don't have any means of measuring the CO2.

KH 5, PH 7.2 = CO2 9.5 ppm

KH 5 PH 7.5 = CO2 4.75 ppm

I'm just using the yeast/sugar water DIY to make CO2, I don't have a bubble counter or anything like that.

[Tech Support LK]

I see. To be quite honest, if you want to run a pH of about 7.0, you will not be able to have a dKH as high as 5. As you probably already know, there is a fixed relationship between pH, KH, and CO2. For instance, in an aquarium with no CO2 injection and an assumed natural CO2 level of 4.5ppm, to keep a pH of 7, the dKH will be very low (about 1.5). Since you are injecting some CO2, you will be able to keep a higher dKH than this and still have your desired pH, but it may take more CO2 than you are currently introducing. This is where the Acid Buffer will come into play. Acid Buffer cuts down the KH by converting it to CO2, thus raising the CO2 level while lowering pH. So, at the end of the day, you have two options:

1) Add more Acid Buffer daily until you lower the dKH around 3. Once you are at that level, in conjunction with your CO2 injection, you should be able to maintain a lower pH.
2) Implement a CO2 injection system that you are able to adjust upward in order to run a higher KH and low pH.

[jdrebit]

Thanks for your response. I was leaning towards adding another 2L DIY CO2 bottle, this confirms it.

I'll just have to sneak it in when the wife is not looking.

[Tech Support EH]

Good luck with that! :)