Re: Water Chemistry Question

[Marc999]

Hello folks,

I am venturing into unchartered territory by deciding to make an attempt at breeding rummy-nose tetras. Therefore, my objective is to create an acidic (pH) and soft (gH) environment for both the rummy-nose and my boliviam rams.

I have researched the basics on water chemistry to gain a better understanding between the bermuda triangle effect of pH, gH, and kH and have the following water parameters on my 20 gallon long fish tank. Nutrafin test kits were used.
I should let you know that yesterday I used a product called Tetra blackwater extract (seems convenient) in an attempt to alter pH and soften the water.

April 2/05: (prior to addition of tetra blackwater extract)
Temp. = ~ 81F
pH = 7.3
gH = 6.72 dH (120 ppm)
kH = 2.24 dH (40 ppm)

April 3/05: (24 hrs. 'after' addition of bw extract)
Temp. = ~ 81F
pH = ~ 6.2 - 6.3
gH = identical to yesterday (calculated to be 6.72 dH)
kH = .56 dH (10 ppm)....yikes, buffering problem present.

I was shocked to see the pH drop so much within such a short period of time; considering these are logarithmic scale calculations, the pH shock to the fish must be incredible.
Question: What is a safe way to increase my kH (to increase my buffering capacity) without altering the pH or gH, since both seem reasonable at this current moment, albeit dramatically lower than 24 hrs. ago.
Postscript: I should mention that I had completed a 50% water change prior to any water parameter testing or blackwater extract additions, so there was certainly no additional water changes within the past 24 hrs.

I have come across different ways to increase kH as follows (notice that the measurements given are drastically different from each other...which is correct???)
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1st source of information:

Ways to increase kH

Adding sodium bicarbonate (baking soda). One teaspoon of baking soda added to 50 liters of water can raise the kH of the water by approx 4 deg dH without a major affect on pH.
Adding an air stone to increase surface turbulence driving off carbon dioxide (CO2)
Adding commercially available products to increase buffering capacity
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2nd Source of information:

To raise the KH without raising the GH, add sodium bicarbonate (NaHCO3), commonly known as baking soda. 1/2 teaspoon per 100 Liters raises the KH by about 1 dH. Sodium bicarbonate drives the pH towards an equilibrium value of 8.2.
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Not only are the tsp. to litres ratios going in opposite directions (i.e. 1 tsp for 50 litres, v.s. 1/2 tsp. for 100 litres....unless it's dependant upon the resulting kH increase value difference), but one method suggested no major effect on pH, while the second source states pH is driven towards 8.2?......I'm confused here.
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Any experts here? I've read and researched much but generally find the internet full of unsubstantiated facts. Of course, the textbooks I've read conflict with either of these aforementioned stats....

Thanks for any help in advance,
Marc

 

[RTR]

I'm not going to write a book about this, but blackwater fish are from low-TDS waters (few mineral ions in the water) with resulting vanishing low alkalinity, plus the water has significant tannins/tannic acid which push the pH down, so the water is quite acidic. BUT (big but) the pH is not the key, the low mineral content (low TDS) is the key. ADDING something to the water will not make the water lower TDS. Water plus extra dissolved material = water with increased TDS, even if the pH is lower. If you want "softer" water, dilute with high-rejection rate RO or RODI.

In the wild, there is massive volume of water per fish. In tanks this is not the case, so we need filters and nitrification bacteria. These bacteria don't work well at low pH/TDS, and tank conditions can change rapidly with too low KH to support the bacteria and the acidification from nitrification. So we cannot match native blackwater parameters easily, but we can lower the GH (calcium and magnesium ions - which are injurious to some blackwater fish's eggs), and the KH to levels which are supportive but still give relatively low TDS.

HTH

 

[wayne]

Surely if you're going to try to breed the tetras you will require low kH (and low Gh, TDS) water. Scared of pH crashes - well say hello to water changes.
Sadly I don't think chemical manipulatio will get you where you want - you did the right thing in the first place.

 

[Marc999]

Thanks for very much for your prompt reply. I was unaware of the negative impact on the nitrifying bacteria at a low pH/TDS, if I understood one of your comments correctly. Yikes, it would seem more important to me to maintain the beneficial bacteria than lower the pH. Hmm, what to do....
Either that or keep up my water changes to increase buffering capacity(generally 1/3 every 3rd day, with a nice gravel vaccumm and 50% water change on either Saturday or Sundays).
The RODI suggestion sounds intriguing, a fine way to soften the water.

Thanks again,
Marc

 

[JosephMCorbett]

Baking soda is commonly used in Marine tanks to drive the Ph up while doing the pre-mix for water changes, and also to drive up the Ph and add buffering capacity to the tank water.