QUOTE: “I don't understand. He says in his answer to a readers question that "the more water changes the better" (up to a point).”

QUOTE: “I don't understand. He says in his answer to a readers question that "the more water changes the better" (up to a point).”

I can see that some hobbyist are confused over the fact that water changes, how much to be taken out and when there carried out can make a big difference in Pollutant Equilibrium (or PE for short) in an aquarium or pond.

The example I’m going to give will show two hobbyists, one we will call hobbyist A and the other hobbyist B. Now hobbyists A will do their water changes every week at a rate of 10% per water change. Hobbyists B on the other hand will do their water changes only once a month at a rate of 40% which equals hobbyists A’s weekly water changes in that same four week span. Does everyone follow me here (10% x 4 weeks or one month = 40%) adjustments will be made for months that have five weeks in them for both hobbyists.

Both hobbyists have aquariums @ 50-US gals and the amount of NO3 being produced by the bacteria will be at a constant of 8-ppm per week for both aquariums. The question is: Will hobbyists A be better productively than hobbyist B because they do more water changes and weekly instead of letting the insults rise too high in a given month?  After all 8-ppm looks a lot better than 32-ppm that hobbyists B has to contend with every month.

This is one thing (water changes) that becomes debatable when in discussion groups and/or forums on the more frequent you do water changes it’s always better than a once a month water change because you do not allow pollution to rise too high in a given time span, right? Wrong! The math shows different! In fact you’re wasting your time and water doing it every week.

Hobbyists A weekly water changes:

Week 1= 8ppm NO3 -10% water change far that week = 7.2ppm of NO3 left for the next weeks water change to contend with plus the 8ppm NO3 that the system will produce for the coming week.

Week 2=(8ppm + 7.2ppm) -10% = 13.68ppm of NO3

Week 3=(8ppm +13.68ppm) -10% = 19.51ppm of NO3

Week 4=(8ppm + 19.51ppm) -10% = 27.51ppm of NO3

Week 5= (8ppm + 27.51ppm) -10% = 31.95ppm of NO3

Week 6= (8ppm + 31.95ppm) -10% = 35.96ppm of NO3

Week 7= (8ppm + 35.96ppm) -10% = 39.56ppm of NO3

Week 8= (8ppm + 39.56ppm) -10% = 42.81ppm of NO3

Week 9= (8ppm + 42.81ppm) -10% = 45.73ppm of NO3

I will stop here because this now shows over two months of water changes and should give us a good idea that NO3 just keeps escalating if not unabated by other means soon.

Hobbyists B monthly water changes:

First months water change will have to contend with 32ppm NO3 because every week it increased by 8ppm. So… 4 x 8ppm = 32ppm of NO3, right?

32ppm – 40% water change (this makes the same as hobbyist A did in a four week span) =19.2ppm NO3 still left.

Month 2= (8ppm x4) + 19.2ppm) -40%= 30.72ppm of NO3

Month 3= (8ppm x4) + 30.72ppm) -40% = 37.63ppm of NO3

Month4= (8ppmx4) +37.63ppm) -40% = 41.77ppm of NO3

Month5= (8ppm x 4) + 41.77ppm) -40% = 44.26ppm of NO3

Month6= (8ppm x 4) + 44.26ppm) -40% = 45.75ppm of NO3

As you can see Hobbyists A after just 9 weeks of 10% water changes is at the same level of NO3 as hobbyists B is after 6 months of water changes @ 40% per month. There’s no debating it, the math does not lie; water changes must be conducted larger than 10% if you really want to do any good to lessen the insults in your aquarium and/or pond.

The only way to lessen water changes in a closed system is with an Anoxic Filtration System.