What's better 50% wc or 25%x2 per week

  • We are currently upgrading MFK. thanks! -neo
25% twice per week creates greater stability...but one 50% water change removes more waste.

If x0 = the initial amount of waste (nitrate) in the tank (mg) and
z= the amount of waste (nitrate) produced per day (mg/day) - assuming constant waste production, and
x7 @ 50% = the amount of waste (nitrate) in the tank after one week in mg

x7 @ 50% = x0 + 7z - .5x0 - .5*7*z
x7 @ 50% = .5x0 + 3.5z

For two 25% water changes per week (on day 3 and day 7):

x3 @ 25% = the amount of waste in the tank (nitrate, mg) after 25% water change on day 3
x3,7 @ 25% = the amount of waste in the tank (nitrate, mg) after 25% waste change on day 7

x3 @ 25% = x0 + 3z - .25x0 - 3*.25z
x3 @ 25% = x0 + 2.25z

x3,7 @ 25% = x3 @ 25% + 4z - .25 * x3 @ 25% - 4 * .25z
x3,7 @ 25% = .5625x0 + 4.6875z

Which is larger (x7 @ 50% or x3,7 @ 25%)?

Assuming x0 = 0, at any rate of waste (nitrate) production, x 3,7 @ 25% is going to have more waste (nitrate) on day 7.

Maybe my math's messed up but makes sense to me :)

Matt
 
JonY3k said:
Do you people have filters on your tanks? Why are your changing your watter so frequently? I normally change the water in my tanks every 2 weeks.
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What's your bio load though,what kinds if fish are you keeping?
 
Filters PRODUCE waste (nitrate)... water changes are to dilute the concentration of waste (nitrate) in the water.

Matt


JonY3k said:
Do you people have filters on your tanks? Why are your changing your watter so frequently? I normally change the water in my tanks every 2 weeks. some times it ends up being almost once a month. I run under gravel filters and canister filters. I have well water so I never treat my water. I fill with 100% cold water because I run the water through a filter so it takes a long time to fill my 150g and 220g tanks back up. I have a float switch that automatically turns the water off when the tank gets full.
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dogofwar said:
Filters PRODUCE waste (nitrate)... water changes are to dilute the concentration of waste (nitrate) in the water.
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Not always since with the right substrate and bio media you can house ANaerobic bacteria which converts nitrAtes into nitrogen. I've also learned at MFK that plants can remove nitrAtes too.

But removing nitrates isn't the only reason to do water changes. Changing water removes things like built up hormones, removes hardness minerals that are left-in/added-to the tank by topping off evaporation, and replenishes minerals and trace elements.

Which might make this wrong:

JonY3k said:
...Why are your changing your watter so frequently? I normally change the water in my tanks every 2 weeks. some times it ends up being almost once a month...
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The easiest way to answer this is as follows:

#1 What is your desired PPM of nitrate? Example 10 PPM
#2 What is the PPM level after 1 week? Example 20 PPM
In this example a 50% water change 1X per week is required assuming your new water has 0 PPM nitrate.
 
50% once will remove more nitrates than 25% twice contrary to what people think. If you start at 100 ppm and do 50%, your nitrates are now 50. If you do 25% your nitrates are now 75. Wait a few days and the nitrates go up and you do another wc starting at 80 ppm. 80 ppm - 25% is 60 ppm.


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