pH and alkalinity issues

[glenna]

Hi!
Well, been working on getting my 125 gallon ready for the fish and the fishless cycle is going great. Eating up the ammonia and nitrites are nil. Nitrates are pretty darn high.
The issue I am concerned about is that the pH is dropping as is the KH.
When I first started the tank the parameters were as follows: pH 7.0, KH 100, GH 75, NO2 and NO3 and ammonia were all neg becasue I had not started the cycle yet. I have been adding ammonia (straight bottle ammonia with only "soft water" and ammonium in it. And of course added some tetra safe start. Did not have enough of that so I have also added some "nitrobacter" (another brand name bacterial supplement recomended by the pet store which they use to start up their tanks).
I started that on Feb 1st and there must have still been some bacteria in the filter and fluorite, on the wood from the last attempt at fishless cycling, becasue it started to show nitrites within a week, and nitrates soon after.
Here is the latest test: pH 6.2, KH 20 (or less!), GH 100, NO2 nil, NO3 90. NH3 1.
WHERE is my KH going and what should I do about it? I know this is supposed to be my buffering capacity and it is not good to have none.
The LFS person told me to add some limestone, which I own, but have not added yet.
any thoughts? is it obvious that I liked chemistry, but am not all that talented in this regard?
help would be appreciated!
tank has black fluorite, temp is 80F, lights are 39Wx 2 fixtures (two if these x 8 hours a day) driftwood, lots of plants
using wet-dry proclear filter with two returns (rio 1700x2)

hope that is enough info

[Diana]

I have no idea where the KH is going, but add some baking soda. 1 teaspoon per 30 gallons should raise the KH by almost 40 ppm. Go ahead and add it right in there, shake it up in a little water, baking soda dissolves pretty fast.

Nitrifying bacteria may be utilizing the carbonates. Do not let it hit 0 ppm. It is OK to add more baking soda as needed to keep the KH at least 60 ppm.

Try the limestone, if you want. If it is powdered or limestone sand or gravel I would try a bag perhaps a nylon stocking. If you like the effect, then this might be added to the filter.
If it is a chunk of rock, or several chunks then add those to the tank. If you do not like the effect, you can remove them.
Monitor GH, KH and pH. Mostly limestone is slower acting than baking soda. It is OK to add both.

Keep adding ammonia to keep it at 3 ppm and keep the bacteria growing and reproducing while we figure out what is going on here.

[glenna]

Thanks, Diana
I was wondering about baking soda, so will add some Today. I have the limestone rocks (fossillized coral) and may add one stone if the baking soda correction does not last.
It is sort of a mystery what is going on in there. I do not have an airstone in that tank. Do you think that would help? (not great for the plants, I guess, as I think that would gas out some of the CO2)
I just want the tank to be very stable before adding any fish.
I will post an update in a few days.
thanks again

[Diana]

An airstone probably would not make much difference, as long as you have filters and power heads running.

The way a limestone rock or chunk of coral work is that the water dissolves the limestone from all the surfaces. On a single rock there is only the outside surface.
On the same amount of limestone if it was broken up into sand it would have a LOT more surface.

Go ahead and add the fossilized coral, but I am not sure how much help it will be. Some, yes.

Another option is to get some oyster shell grit that is sold for caged birds. The finest pieces are like sand, and would have a lot of surface area. (In a pet store, sold for small birds like Budgies). Put a handful or two of this in a nylon stocking and add it to the filter.

[Graeme McKellar]

Hi Glenna and Diana,
I have been watching this thread with interest as I have had the same problem before with almost zero KH and a PH dropping below 6 and was advised to add Aragonite chips directly into the filter basket.
This solved the problem for me and PH and KH levels are all stable.
Cheers Graeme.

[Diana]

Graeme, what about the GH? Did it rise when you added Aragonite?