So I'm pretty new to aquariums, but old to chemical engineering. If you think about an aquarium like a chemical reactor the food would be the reactant, the nitrate would be the product, and the fish / bacteria would be the catalysts. In that regard it is easy to calculate how much water to change, if you measure a few things first:
First pick a time frame, how often you want to change the water
Next, measure the nitrate build in your tank over that period of time
Then decide the max nitrate your fish can tolerate and be healthy
Finally, use this math
I = initial nitrate level (ppm)
G = gain in nitrate over your period of time (ppm)
F = Final / max nitrate level (ppm)
V = volume left after water is removed
Then we have
I + G = F, rearranged gives I = F - G
At steady state we want F x V = I so that it is the same change after change
substitute in you get F x V = F - G
So then solve for V = (F - G) / F
Water change % = (1 - V) *100%
For example you measure G to be 10 ppm per week and your max level is 40ppm
V = (40-10)/40 = .75 => % = 1-V *100% = 25% water change per week
This is assuming nitrates are the key thing to determine water changes.
Also, clearly, the G will change as your fish get bigger, so will need to be re-measured occasionally.
I just decided to do this because of all the threads asking for advice on how much water to change, and people seem to respond with pretty wild guesses based on their UNIQUE system. I looked for something like this and couldn't find it, if it's already been done o well. So the big question then becomes what F should be, and if you read the first sentence I'm way too new to aquariums to know that.
Any thoughts?
First pick a time frame, how often you want to change the water
Next, measure the nitrate build in your tank over that period of time
Then decide the max nitrate your fish can tolerate and be healthy
Finally, use this math
I = initial nitrate level (ppm)
G = gain in nitrate over your period of time (ppm)
F = Final / max nitrate level (ppm)
V = volume left after water is removed
Then we have
I + G = F, rearranged gives I = F - G
At steady state we want F x V = I so that it is the same change after change
substitute in you get F x V = F - G
So then solve for V = (F - G) / F
Water change % = (1 - V) *100%
For example you measure G to be 10 ppm per week and your max level is 40ppm
V = (40-10)/40 = .75 => % = 1-V *100% = 25% water change per week
This is assuming nitrates are the key thing to determine water changes.
Also, clearly, the G will change as your fish get bigger, so will need to be re-measured occasionally.
I just decided to do this because of all the threads asking for advice on how much water to change, and people seem to respond with pretty wild guesses based on their UNIQUE system. I looked for something like this and couldn't find it, if it's already been done o well. So the big question then becomes what F should be, and if you read the first sentence I'm way too new to aquariums to know that.
Any thoughts?
