CO2, KH,pH

[jonathan11]

Guys,
I'm having a problem with my 180. I have a KH of 10-20 ppm. My pH both on my meter and a cross check with my test kit says 7.2. This pH has dropped over the last few days, to 7.2 after a 30% w/c, where the pH was initially at 7.6. I do not use any pH up/down. I do add mono potassium phosphate and potassium nitrate periodically as macro ferts, with TMG for micros. My nitrates measure 10-20 ppm, with my phosphates at 2 ppm. I'm perplexed-how can I have a pH at 7.6, and a KH at a low point of 10-20 ppm. I have seachem black sand as a substrate, which I thought might be buffering somewhat. My calcium test kit seems to be kaput, but I'm fairly sure it isn't a calcium carbonate issue, but I will get a new Ca kit.
I'm hesitant to start pumping CO2 into the tank-according to the chart, the pH will need to be dropped quite a bit to get 20-30ppm. I have a CO2 indicator (somewhere) that I'll resurrect, but I still have my doubts-and fears my fish will go belly up if I pump the CO2 into the tank.

All suggestions would be greatly appreciated. Thx in advance,

Walter

 

[Tom Barr]

Respect the gas, do not fear it.

Progressive slow approach to increasing it WHEN you are around to observe the fish.
My KH is soft like yours, my light is likely higher.

I tend to knock the pH in the high 5's and 6.1 ranges.
You can target 6.3 and then slowly adjust from there.

If the KH is 20 ppm or about 1 degree..............there's nothing that will give you a false reading UNDER this, so it's fairly safe to assume of that small amount of KH, most is likely bicarbonate.

 

[jonathan11]

Many thx, Tom. Will do.

Walter

 

[Tom Barr]

In other words, the pH/KH/CO2 chart should be very close/accurate with such low KH's.