Formula for water change calculator

[Maivortex]

What does RPNG stand for and what is the formula used to calculate RPNG

http://www.reefcentral.com/calc/RODICalc.php

[HighlandReefer]

I have to admit, I don't understand this calculator & what it is calculating. :(

Perhaps it is calculating the reduction of unwanted nutrients in a given tank volume by doing water changes?

[kkil4life]

highland, I think its......
Week % Pure % Non-Pure PG NPG RNPG

thats week number, % of pure water, % of OLD water, Pure Gallons, Non Pure Gallons, Replaced Non Pure Gallons

[Maivortex]

How does one calculate the "Replaced Non Pure Gallons"?

[HighlandReefer]

Randy discusses your answer in this article:

Water Changes in Reef Aquaria
http://reefkeeping.com/issues/2005-10/rhf/index.php

From it:

"The extreme case of infinitely small water changes done an infinitely large number of times is approximated by continuous water changes that add water at exactly the same rate it is being removed. The details of how to do this mechanically are described below. This case is a standard example in advanced math textbooks (differential equations, specifically). Assuming the aquarium is well-mixed as the water is changed, the remaining impurities are given by:

I = Ioe(-C/T)

where I is the amount of impurities present, Io is the amount present at time zero, e is the constant 2.71828, C is the amount changed, and T is the tank’s total volume. So for 30 gallons changed this way in a 100-gallon tank, the remaining impurity is 0.74 times Io, or a reduction of 25.92%.

The table below compares these results for a 30% water change done via different numbers of smaller changes. Clearly, the single 30% change is a little better than the others (70% vs. 72-74% initial impurities remaining), but the difference is quite small, and the difference between the others in efficiency is trivial."

[Boomer]

Look here guys for WC calculators and many more :)

http://www.hamzasreef.com/Contents/Calculators/index.htm

[HighlandReefer]

Nice calculators, Boomer. :)

[Boomer]

Yes Cliff and thanks. We have spent months on these trying to make them better or more accurate, easier to use and with updates. The H is a mathematician and reefer :D He often posts here also. I more or less find data for him or equations. More than a year ago he asked are there any calculators I would like to see ? I said are you SURE you want to ask me that question :lol: Me, the calculator freak. He is worse than me. And The H is always trying to dream up new ones also :D

[HighlandReefer]

Big Thanks to the both of you for all your hard work. :D

[mr.maroonsalty]

SWEET! Boomer, Thank you! and to H too!