Maintaining pH

[connie08]

Hi,

I'm growing this algae called coccolithophorid algae for a project. I'm trying to see how it grows in certain levels of pH. The range that I'm testing is from 6-10. How can I change the pH level without killing the algae and how can I maintain the certain pH level?

Thanks.

 

[bluerose]

I believe you can add baking soda or crushed coral to raise pH... lowering, though, might be tricky.

Aside from pH you should keep gH and kH in mind as well-- levels of dissolved minerals in the water, etc. Starting with distilled water and then adding solutions to alter pH would probably be easiest.

What kind of project? (I'm a science geek.. )

 

[jsoong]

The only way to have a stable pH would be to set up a buffering system with the desired equilibrium pH. Just adding strong acids or base to water will not give you enough stability unless you have some kind of continuous dosing with a feedback loop. You prob should start out with distilled water & add an appropriate buffer to get to a certain pH.

You can use CaCO3 for pH 7.8-8. That happens to be the equilibrium pH for a carbonate buffer. The lfs store sells buffers for cichlids that would give you a higher pH, and neutral or low pH buffers. For a science project, I would suggest researching buffers & choosing ones that will work. Of course, the buffers themselves can't have an effect on algae growth, so phosphates, nitrates, CO2 are prob out. <If the algae do biogenic decalcification, than carbonates may throw things out too ....>

Depends on how sophisticated your experiment is as to how you might want to set up things. To get really good results, you would need quite a few controls for the various minerals in addition to the pH.

 

[connie08]

It an environmental science project.

Would adding baking soda/crushed coral daily maintain the pH?

 

[connie08]

So I have to use distilled water? Before, I was just going to use tap water. And is this going to be expensive because the algae is already costing me around $100.

 

[bluerose]

I don't think you have to use distilled, but if you need, say, three different pHs, it would be easier (and probably more scientifically accurate) if you started with distilled.

Depending on your tap water you may have a pretty stable pH already.

Of course, it depends on how exact your results need to be and how you're running the experiment... as jsoong said there are varying additives that mess with pH but would also influence algal growth.

 

[Blueiz]

The trouble with using tap water is the buffers in it and trying to lower the ph to the approprate level. This is very hard to do and maintain it unless you use something natural like peat. If you are lucky enough to have a low ph already, it won't be as difficult as it will be if you have a high ph.

I agree with using distilled water, this will keep the integrity of the experiment because you wont have other facotrs to look at, such as the amt of nutrients in the water, etc.. especially if you are on a municipal supply.

You don't have to add crushed coral daily, you just replenish it when it dissolves..

 

[jsoong]

It depends a lot on what your source water is if distilled is needed ....

Thinking about it some more ... Algae is not going to thrive in just distilled water + buffer. It is going to need nutrients. If your tap water isn't too bad (ie liquid rock!) you can prob use tap + nutrient as your control.

Eg. You can decide to use a complete hydroponics fertilizer as your nutrient base. Mix up an appropriate concentration of the fert + tap & call that your control #1. That will have an intrinsic pH. The fert solution is a buffer in its own right, so might keep that pH relatively steady. However, as the nutrients are used up, the pH might shift. You are going to have to monitor that & may have to do some additional dosing to keep things constant. <You will have to dose all your experimentals the same way if dosing is needed. ... This si going to depend on length of the experiment ... you prob have to dose the ferts if it lasts more than a few weeks.>

Now that you ahve your control, you will have to vary the pH somehow. Altering the buffering system (eg adding crushed coral = CaCO3, etc) is the most fool proof way. But I really can't think of any buffering system that is also not physiologically active & skew your result. Even HCO3 may have a effect if the algae is capable of biogenic decalcification. You could do a double control ... Eg adding NaHCO3 to one to raise the pH & H2CO3 to another to decrease it, that controls for the HCO3, but not the Na ....

You might try maintaining the different pH by adding strong acid or base. Ideally, you would need a constant feedback loop & some form of auto dosing equipment, but with the fert solution acting as buffer, you might get decent stability if you manually adjust things daily. Say, you add Ca(OH)2 to raise the pH (vary the amount to increase to different pH ranges) & HCl to decrease pH. Check daily & adjust your experimental tanks so the pH is within range. To account for Ca & Cl, you would need a second control - fert + CaCl2 only. <Since Ca & Cl are both in the balanced fert solution, chances are this will be the same as control 1, but do it just to be through.>

I don't know if the daily pH adjustment is adequate, nor if your tap water is suitable for this. <Some miniciple water is already doctored with CaO or Ca(OH)2 +/- HCl. Others are way too hard (too high KH) for you to easily change the pH with acid/base.> You might want to do some preliminary tests on the various water combinations to see how it pans out.