Why a weekly 50% WC is better than two weekly 25% WCs

[ScatMan]

Alright, now I think I understand what your trying to say...though the nitrate levels would be higher without doing the filter cleaning/gravel vac they would be affected in the same way as described on the spreadsheet. Meaning they would be decreased at the same rate...right?

you got it brother! i love you now! but not the same rate, the respective rates of the 2 water changes. each wc method would give you different rates of cleaning, the 1 50% being slightly better than 2x 25%.

 

[DavidH]

This is my first post on this forum, but I have to say, I grew INCREDIBLY frustrated reading through this thread and seeing people that were so determinedly and blatantly dismissing BASIC math.


One thing is not understanding, which is cool... but some here are just arrogantly dismissing things (and throwing in smileys) because they don't understand them, rather than trying to understand or ask constructive questions.

Anyway, kudos to the thread starter and everyone else who constructively contributed to this thing.

 

[jlnguyen74]

what does that have to do with the formula? nobody is arguing what you're saying.

That's one of unknowns that the formula doesn't take into consideration. The longer waste sit in the tank, the more nitrate produced. The OP assumed the nitrate increase at a constant rate of 10ppm per 3.5 days, and 20ppm per 7 days. Unless he takes actual test, that rate should be "x" amount per day.
Assume two tanks with same bioload, same filtration, same feeding schedule with no food left behind, same everything, start at 10ppm
If you do weekly 50% water change:
At the 7th day, fish will be exposed to nitrate of 10ppm + 7x
Once you do the 50% wc, nitrate will be at level of 5ppm + 3.5x, assuming wc removed 50% of everything.

If you do 25% wc, twice a week:
At the 3.5th day, fish will be exposed to nitrate of 10ppm + 3.5x
After you do 25% wc, nitrate will be at level of 7.5ppm + 2.6x, assuming wc removed 25% of everything
At the 7th day, fish will be exposed to nitrate of 7.5ppm + 6.1x
After you do the second 25% wc, nitrate will be at level of 5.6ppm +4.6x

Only after you do the 50% wc and the second 25% wc, the nitrate level of the first tank is lower than the second tank. However, the fish in the first tank is exposed to higher level of nitrate than the fish in the second tank. If you have time, continue that "formula" and find out what happen in 2nd week, 3rd week, and so on... Of course, that's still not mathematically proven, since there are many "assume" in that "formula"

 

[jlnguyen74]

no, it is a mathimatically proven fact.

like flipping a coin has a 50-50 chance of landing on any particular side. it's mathematically proven. you could test it by flipping a coin 1,000,000X and counting the # of heads and tails but you don't really need to.

So, if I flip the coin 1,000,000 times, how many heads and how many tails as provent fact that I'm going to get?

 

[jlnguyen74]

What a wonderful thread full of unsubstantiated claims and dismissal of basic math.

This is my first post on this forum, but I have to say, I grew INCREDIBLY frustrated reading through this thread and seeing people that were so determinedly and blatantly dismissing BASIC math.


One thing is not understanding, which is cool... but some here are just arrogantly dismissing things (and throwing in smileys) because they don't understand them, rather than trying to understand or ask constructive questions.

Anyway, kudos to the thread starter and everyone else who constructively contributed to this thing.

No one dismiss BASIC math. However, it is what it is. BASIC math is BASIC! Life is not!!

 

[JteSchertz]

Well I have one problem tank right now(my growout)...gonna try the 50% per week to see if it helps. Thanks for putting up with my confusion!!!

 

[vfc]

That's one of unknowns that the formula doesn't take into consideration. The longer waste sit in the tank, the more nitrate produced. The OP assumed the nitrate increase at a constant rate of 10ppm per 3.5 days, and 20ppm per 7 days. Unless he takes actual test, that rate should be "x" amount per day.
Assume two tanks with same bioload, same filtration, same feeding schedule with no food left behind, same everything, start at 10ppm
....

I managed a group of engineers and you remind me of a couple of them who suffered from "analysis paralysis". They would hang on to some little detail (like looking at all the trees; arguing over the randomness of the space between them, and not realizing they are in a forest). They wasted a lot of time in our group meetings.

To help you get over your paralysis; please keep in mind the OP's original post used an AVERAGE of 3ppms per day to show how weekly 50% WCs maintain a lower AVERAGE ppms per week.

Sure any given day the ppms will vary from the average 3ppms/day. Some days you will feed more and the next day ppms may be 4. Occasionally you clean the filters and vacuum the gravel; those days the ppms may be 1 to 2. Some weeks you may average 2.5ppms; other weeks it may be 3.5ppms.

However, over a longer period of time, the average for the OP's tank will be 3ppms/day; and the 50% weekly WCs will be better.

Now knowing your over-analysis tendencies; I suspect you will go make a manual calculation with daily varying ppms. Take 70 (10 weeks) random numbers varying from 0-6(ppms) that average 3. Manually calculate the nitrates for each of the 10 weeks with 25/2 and 50/1 WCs, then average up the results. You will find that the results will be the same as the OPs results.

 

[JTRG05]

There are so many people arguing this thread. What exactly IS the conclusion?

And wouldn't the average of 25% water change on the end of the 3rd day have a lower average ppm than that of 50% water changes at the end of the 7th day?

At the end of 14 days I observed an average of 24.620 for 25% changes, and 25.625 for 50% changes. I used a runaway ppm amount, 5ppm per day increasing, could it be in heavier stocked tanks with higher ppm increases the smaller more often water changes are more effective, or are they in general? Is my math wrong or is this in support of the previous data?

In any case my 6 neon tetras in my 55 gallon don't need much of a water change...

 

[DavidH]

So, if I flip the coin 1,000,000 times, how many heads and how many tails as provent fact that I'm going to get?

You're going to get 500,000, give or take an extremely small and marginal amount for error.

In the long run, given adequate sample size, statistics and numbers don't lie. Statistics are the truth.


Go ahead and try it in practice if you want. Let us know how it goes.

 

[vfc]

There are so many people arguing this thread. What exactly IS the conclusion?

And wouldn't the average of 25% water change on the end of the 3rd day have a lower average ppm than that of 50% water changes at the end of the 7th day?

At the end of 14 days I observed an average of 24.620 for 25% changes, and 25.625 for 50% changes. I used a runaway ppm amount, 5ppm per day increasing, could it be in heavier stocked tanks with higher ppm increases the smaller more often water changes are more effective, or are they in general? Is my math wrong or is this in support of the previous data?.....

Your calculations are correct. However, starting with 0 nitrates, it takes about 40 days for the pattern to normalize. See attached charts with your parameters (5ppms/day, start with 0 nitrate). 50% weekly (I use 6 days) has a lower nitrate average than the 25% every 3 days.