bicarbonate and the fishless cycle

daveedka, this is a fun problem!

In reference to what happychem was saying:

Let's say you change your water by 30%, leaving 70% behind with the 'stuff' you added, whether salt or what have you.

Let k be the amount (fractional) of water you leave behind.

Let Ci be the concentration after ith addition of salt or stuff.

Let x be the amount of stuff you add, arbitrary units (mg, mol, drops, whatever).

Let V be your tank volume.


If C0=0 (nothing in there to start with), after 1 addition you get C1 = x/V.

Now you remove (1-k) fraction of water, leaving k fraction behind. The total amount of your stuff left in the tank is k*C1*V. Also, we're adding x more when we do the water change. Therefore C2 = (k*C1*V + x)/ V or
C2 = (k+1) x/V.

Similarly, C3 = (k*C2*V +x)/V and if you use the recursion relation you get
C3 = x*(k^2 + k +1)/V, C4 = x*(k^3 +k^2 + k + 1)/V ...etc.

You can go ad infinitum. The ith addtion/water change gives you

Ci = x * (1 + k + k^2 + .... k^(i-1)) / V

This is a geometric series and can be written in closed form:

Ci = x*(1-k^i)/(1-k)/V

The steady state is given by summing to infinity. You get

Cinfinity = x/(1-k)/V

So now let's put in numbers. If you're doing a 30% water change every day and adding 0.5 g of baking soda to a 55 gallon tank (210L), after many many changes you get

Cinfinity = 0.5 g / (1-0.7)/ 210 L =
0.5 g / 0.3 / 210 L = 0.0079 g/L or ~ 8 ppm of your baking soda.
 
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To return to your original question, happychem, adding baking soda or other sources of bicarbonate can also help keep the cycle moving along in conditions of low KH tap water. The addition of bicarbonate helps prevent pH crash as KH is used up (rapidly) during the fishless cycle. This is important, because as pH drops the bacteria become less and less active. As pH drops below 6 oxidation slows greatly and stops, I think, about pH of 5.

Adding bicarbonate helps prevent the pH crash by buffering the water against pH changes, in addition to whatever cellular needs the bacteria may have for it.

Jim
 
well this morning's test revealed that i still have about 5ppm of ammonia, and the nitrite and nitrate is off the charts.

so im gonna let it be for the rest of the day (not adding any more ammonia) and test it again this afternoon/evening.
 
silentskream,
what are your KH and pH, both before and after if you have them for before. Remeber that this will only help if your KH is crashing, not to mention, it will only help if you actually have the bacteria present.
 
id ont have a KH test. but the pH has been steady at 7.2

i definitely have the bacteria present, theres gravel from an established tank, a filter cartridge from an established tank, and a 12 inch air stone from an established tank. and up until i had these items in there, i had no nitrites/nitrates whatsoever.

in addition i have a sword plant,
 
Gotcha.

You should definitely get a KH test kit, especially if you're interested in growing plants (read CO2).

Is 7.2 the pH before or after the bicarbonate addition? I'm guessing it must be before if you're talking steady. But if your pH was steady throughout the cycling process, you probably aren't KH limited so the bicarbonate probably won't help.

Wow! look at all those indefinites, I must be a scientist or somthin'...;)
 
That is very odd.

Although the cycling process would lead to that, I would have expected the addition of baking soda to increase your pH. Hmmm...

Ah, 55g is a lot of water. Out of interest and for your future info., it may be worthwhile to find out how much your tank pH changes for a given addition of baking soda.
Add a bit, maybe a tsp. or a tbsp., give it some time to mix, so depending on the circulation in your tank, then test pH again.

As an aside, adding baking powder will have double the effect of baking soda.
 
blah. maybe i'm doing this wrong
Click to expand...

Or Maybe you're doing it right:D , What is your water PH after sitting out for 24 hours, and before adding the baking soda, also what is the water PH after setting out for 24 hours and adding the baking soda. One of the things I have figured out is that it takes very little baking soda. My water takes about 5ml for 30 gallons to raise the KH 2 ppm and raise the PH .2 If you added two TBSP to a 55 and you are still having PH drops, I would think you started out pretty low just at a glance.
DAve

brendanh, Thanks for the equation, I'll punch in my numbers and see if I have anything to worry about in the first ten years.

Also does someone know the actual make-up ratio of baking soda. i.e. how much sodium is in a teaspoon of baking soda.

Wow, my head may start hurting if I'm not careful.
 
my ph for the last week or so has been about 7.2

then after putting baking soda in there i left it alone for about eleven hours, and my ph was 6.8ish

that just doesnt make any sense. if anything the baking soda should have SLOWED the change in ph, but it didnt.

anyways.. like i said before i'm just gonna let it sit for a little longer, the ammonia is high, so i didnt add any more, and i'm going to test it again later today. maybe around 2 this afternoon it'll stop being stupid and start doing what its supposed to:p
 
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