This reference will help you

http://www.google.co.in/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&ved=0CEEQFjAC&url=http%3A%2F%2Fjoneschemistry.wikispaces.com%2Ffile%2Fview%2FChalk%2BLab.docx&ei=KVEHUeSWIcTMrQfjtIDIBg&usg=AFQjCNF7kx6HIuCMN7gnxApfP0npUTN27Q&bvm=bv.41524429,d.bmk

I don't know why are you using calcium carbonate as carbon source in aqueous medium, why not sodium or potasium carbonate, they are soluble.

Substitute the equivalent amount of sodium carbonate

I'm with Patrick. The solubility is very low, and your milkiness is probably undissolved CaCO3. You could either throw it all in there and filter it off (but your concentrations will be about 13 mg/L at 25C, or just saturate your solution with CO2. The solubility of CO2 in water is nearly 1.5g / L at 25C. Some of the CO2 will react with water and make CO3^2- the rest will be CO2. Then assuming there's no direct reaction between your bacteria and CO2 you have a much larger supply of CO3^2-. As you use some up more will form. Just keep an eye on the pH. If you need to just throw in a phosphate buffer.

If your bacteria survive at lower temperatures, ice down your solution and increase the solubility even further.

Oh, make sure your system is sealed. Otherwise you'll lose a lot of the CO2 to the atmosphere.

Last thought, I promise. That also gives you a "green" angle to play when you're publishing.

Dear Francisco,

I have been going also through the other posts and found some inconsistency of at least the solubility of calcium carbonate in water, which should be 0.0013 g/100 mL (25°C). Other sources state: "47 mg/L at normal atmospheric CO2 partial pressure" (cf. http://en.wikipedia.org/wiki/Calcium_carbonate#Solubility_in_a_strong_or_weak_acid_solution) or "Calcium carbonate has a solubility of 14 mg/L, which is multiplied by a factor five in presence of carbon dioxide", cf.

( http://www.lenntech.com/periodic/water/calcium/calcium-and-water.htm ). You also did state in your question that you Ca-carbonate by diluting it 1:1 with HCl, but you did not mention

i) concentration / endvolume of the Ca-Carbonate solution and

ii) whether the HCl was diluted or not (if diluted, what was the end concentration compared with the end concentration of Ca-Carbonate in solution?).

Could it therefore be that you used (too highly) concentrated HCl instead of dilute HCl? I have tested the following: 0.1 g CaCO3 [eg. Merck # 2066] added to 100 ml A. bidest (@ RT, clearly the powder will not dissolve, also not after 5 min Ultrasonic treatment). Then I added 4 times each 1 ml of 0.2 N HCL (swirling intermittently) which yielded (at least for my eyes) a clear solution without gas bubble formation (but perhaps CO2 was formed unvisibly) . The pH (proved by lackmus/litmus stripe) shows weak acididity of the solution (litmus slightly red if not pink) guessing to be around 5 - 5.5 - 6, not measured by a pH meter). The solution was stable at least for one hour at RT. Hopefully I will not be tarred and feathered for this.

oxidizing bacteria of manganese and iron？Are these bacteria chemoautotrophy ? You can use the NaHCO3 as the carbon source if the pH of solution was more than 6.00. But if the bacteria could attach the surface of CaCO3 prills, these bacteria maybe utilize the carbon along with the prills dissolving just like bioleaching. I concentrate on bacteria related to Fe, Mn, Cr and Cu, we can communicate with each other.

Try to use soluble calcium bicarbonate Ca(HCO3)2,also called calcium hydrogencarbonate. Its natural compounds that presents in the natural water after erosion of limestone (CaCO3).

You have not mentioned the concentration units etc. what is the strength of sol. required by you?