Scapexghost Posted May 22, 2022 Share Posted May 22, 2022 (edited) The power just went out so it seems like as good a time as any to talk about water changes. First, let's determine if a 25% water change every week is equal to a 50% every other week. At first, some may think that they are the same, while others will say that the 50% change is greater. In the case of the 50% water change, 50% of the original water is replaced. In the case of the 2 25% water changes, 25% of the original water is replaced, and then 25% of the 75% remaining original water is replaced, meaning the 2 25% water changes is only equal to a 43.75% water change. However, there is more to it. This is because the nitrate levels in the tank are changing. So, let's map this out. Let's take 2 tanks, both producing 10 nitrates per week. The first tank we'll do 25% weekly water changes while the second we'll do 50% bi-weekly changes. At week zero, both tanks have zero nitrates. At the end of week one, both gain 10 nitrates. In tank one, we remove 2.5 nitrates, leaving 7.5. In tank two, we remove no nitrates, leaving 10. At the end of week two, after the water changes, tank one now has 13.125 nitrates and tank two has 10. After week three, tank one haa 17.34375 nitrates and tank two has 20 nitrates. After week four, tank one has 20.5078125 nitrates and two has 15 nitrates. Let's stop for a moment, as two things are becoming appearant. First, it shifts back and forth between the two tanks as to which has more nitrates. Second, both tanks are increasing in nitrate levels despite the water changes. This is concerning, as it looks like the nitrates will keep increasing forever regardless of how many water changes we do. But will they? Let's see. In tank one, the nitrates are increasing by 10 every week, and decreasing by 25%. So, the change in nitrates is equal to 10-.25N, with N being the number of nitrates in the tank. If we set this equal to zero, we can see what the nitrate level will be once the nitrates no longer change. So, 0=10-.25N, and N equals 40. So, the max nitrates in this tank are 40, and the nitrates will never pass this amount. So, what about tank two? Well, the formula for this tank is 20-.5N, and N will once again equal 40. So, in terms of maximum nitrate levels, a 25% weekly water change is the same as a 50% bi-weekly water change. We can also use this formula to determine the ammount of water changes we need to do in any tank. Lets say n is the ammount of nitrates produced per week, N is the max ammount of nitrates we wish to allow, and x is the % of water we need to change to achieve this. So, the equation is 0=n-Nx. Solving for x, we get x=n/N. Hopefully this helps answer the age-old question "how much water should i change," and clear any confusion around more, smaller water changes versus fewer, larger water changes. Edited May 22, 2022 by Scapexghost Added graph, added paragraphs 2 1 Link to comment Share on other sites More sharing options...
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!Register a new account
Already have an account? Sign in here.Sign In Now