WC more than 100% any point? or just a waste

[henward]

ok,

technically, if your wc regime chanes about 100% water a week, is there much point of doing more? is that just a waste?

technically, 100% means just that, the whole tank water is changed during the month.

so if you change it more, then you are not really doing much to the water but cooling it.

is this right?

[smidey]

i have always wondered one thing about the constant water changes. How effective are they if you don't actually remove water before replacing it? Normal process is to remove say 30% of the water and replace it which would make a large difference but with a constant water change it must only dilute it slightly. Are there any actual facts on how effective it is?

[Squirt]

Look at it this way

You have 100ppm Nitrates.

You do take 25% of the water out and replace it with 0ppm nitrate water

Essentially you are left with tank water at 75ppm nitrate water

Constant water change, I assume means an auto WC system. So say you have a 100L tank and this system does 1L water changes an hour. Your tank has 100ppm nitrates

One hour later 1L is changed out therefore at that point and time you have 99ppm nitrates assuming no waste is produced by fish

Another hour later another 1L is changed. Then you have 98.1ppm nitrates.

The another hour later another 1L is changed you then have 97.119ppm nitrates

This is a sort of dis exponential curve of total nitrates.

Start is xppm after one hour it is less xppm - .1x, another hour (xppm-.1xppm)-.1(xppm-.1xppm) ect

[GrahamC]

This is like one of Zeno's paradoxes ... you can't do a 100% water change thru infinite partial water changes. But of course you can.

You have to look at why you are doing the water changes for, and whether the frequency of those changes achieves the desired effect.

[henward]

oh, i can account and testify to the effectiveness of auto wc system i have.

My n itrates rae NEVER higher than the second colour on the tester kit. IN fact, i hardly ever see it past the first colour. if i remember correclty, 15ppm is consdiered high in my tanks.

i can vouch for the effectiveness, also the good thing about it is that the auto changer system avoids any spike in nitrates.

so instead of the nitrates reaching say 50ppm in my tank, it never does, it fluctuates from almost none to just about 15 ish.

also the advantage of this is that IF in the event that you have a possible amonia spike.

it dilutes that and gives you an added margin.

Say my current changer setting does about 300L to 350L a day over 24 hours period. my system is 2000 litres total.

so if there was a possible spike that the 3x fx5 and massive sump could not handle. then i have a 15 to 20% wc in the day that will give me that safety margin. (as you know i feed a fair amount)

i guess i am wondering, is it worth doing much more than 100% wc a week.

i guess in theory, there isnt. cos the entire volume of the water is displaced weekly.

as for water trickling in, amonia, nitrite and nitrate are all dissolved in the water, which means it is diluted, so by putting water in and removing it automatically, it dilutes and disperses into the system, thus reducing the contaminants.

[GrahamC]

It sounds like you have the nitrogenous wastes covered better than most of us with your automatic water change system.

Theoretical question, is there any possibility that you might be adding heavy metals faster than the plants can cope with removing them?

[henward]

I dont have plants in the tank.

i find the water from okura resevoir is very good.

i dont age it or treat it. havent done so for years now.

[David R]

I'd say it depends over what time frame the 100% is changed. Obviously you can't do more than 100% at one time, but you could do 30% daily which adds up to 210% a week. If your waste parameters are all good though changing more water isn't really going to achieve much, you're literally just flushing money down the drain.

As for the constant vs large and less frequent changes question, there is obviously a happy middle ground where the frequency and amount changed are most efficient at diluting waste. And I'd think Henwards system doing a couple of daily changes is probably pretty close to it.

[hovmoller]

Look at it this way

You have 100ppm Nitrates.

You do take 25% of the water out and replace it with 0ppm nitrate water

Essentially you are left with tank water at 75ppm nitrate water

Constant water change, I assume means an auto WC system. So say you have a 100L tank and this system does 1L water changes an hour. Your tank has 100ppm nitrates

One hour later 1L is changed out therefore at that point and time you have 99ppm nitrates assuming no waste is produced by fish

Another hour later another 1L is changed. Then you have 98.1ppm nitrates.

The another hour later another 1L is changed you then have 97.119ppm nitrates

This is a sort of dis exponential curve of total nitrates.

Start is xppm after one hour it is less xppm - .1x, another hour (xppm-.1xppm)-.1(xppm-.1xppm) ect

Good math Squirt!

Henward I think you should set up an experiment:

Set up a tank with water only and add something that can't dissipate or evaporate (eg salt)

Meassure concentration to start with, then do "100%" water change over a week by continous drip and then remeassure the salt concentration.

I'm sure we will all be very interrested in what you find.

[GrahamC]

It's a bit more complicated as there is an unknown rate of nitrate generation in the tank.

[hovmoller]

It's a bit more complicated as there is an unknown rate of nitrate generation in the tank.

Which is why we need a controlled experiment to start with.. then we can speculate on other build ups after that. :thup:

Squit is excactly right.. assuming the new water is zero in everything except water then any concentration in the tank is a decreasing exponential curve.

Where you end up after having dripped in the same amount as your tank? who knows... but it will be quite far from 0

[GrahamC]

The mathematical model above assumes that the water being removed is all old water, but if you have a continuous water change system, you may be removing some new water with the old water. It will still be an exponential decay process and the difference this makes may be negligible

[Squirt]

The mathematical model above assumes that the water being removed is all old water, but if you have a continuous water change system, you may be removing some new water with the old water. It will still be an exponential decay process and the difference this makes may be negligible

Hmm

But what would remove more nitrates:

2x25% water changes; so you do 25% add new water then another 25% and then add new water (this is essentially what a continuous water changing system is doing but on a smaller scale (add one drop one drop goes out). Eg 100ppm nitrate water, 25% water change and add new water 75ppm nitrate. Then another 25% water change and new water added in. You now have 56.25ppm nitrates

Or

1x50% water change? Eg 100ppm water one 50% WC and then you have 50ppm water.

It is clear which method is more effective. Changing out the same amount of water.

[blueether]

Hmm

But what would remove more nitrates:

2x25% water changes; so you do 25% add new water then another 25% and then add new water (this is essentially what a continuous water changing system is doing but on a smaller scale (add one drop one drop goes out). Eg 100ppm nitrate water, 25% water change and add new water 75ppm nitrate. Then another 25% water change and new water added in. You now have 56.25ppm nitrates

Or

1x50% water change? Eg 100ppm water one 50% WC and then you have 50ppm water.

It is clear which method is more effective. Changing out the same amount of water.

A good way to look at a auto WC is this, you are adding the water before removing any:

100l tank at 100ppm of nitrate (or salt etc) (lets keep the math simple )

add 1l of 0ppm water and stir

nitrate (or salt etc) is now at 100/101l or 99.009901ppm just above Squirt's example

Now remove the added 1l and start again

I can't be bothered to work it out but I would think it works out to be close to 50% reduction for each 100% WC

[Jaxxnz]

In the past 4 months I have been try out this WC method: Garden hose in" by input clean water in and syphon waster water out at the other end..

To me auto Wc isnt a good method, because you will discharge clean water at the same time..money down the drain x2..

also its take me longer to work on my tank..i suppose it only good when water temp doesnt spike so quick..

I only try this because it less hassle for me to shut off the sump pump//

Has any one ever try setting up a WC system like Toilet Cristern System"? one flush could drain out 30-50% of tank water... :thup:

I am very interested in setting one up in my next monster tank project.. :digH:

[R32GOTMLK]

To me auto Wc isnt a good method

depends on how u set it up

ive got mine so it drains first then it fills

[David R]

1x50% water change? Eg 100ppm water one 50% WC and then you have 50ppm water.

It is clear which method is more effective. Changing out the same amount of water.

It may be more effective at diluting waste on paper, but you have to take into consideration the fact that an aquarium will have ever-increasing nitrate levels. Draw a line graph showing nitrate levels over time and compare the increase/decrease while doing 100% changes every two weeks, 50% changes every week, 7.14% daily change and 0.3% hourly change you will see that although the larger less frequent changes are more effective at reducing the nitrates, if you're changing the same amount of water in larger less frequent lots the nitrate levels will get higher between changes than they would with smaller more frequent changes.

The thing with a contiunious or automated system that makes small additions of clean water at regular intervals (like Henwards) is that although they may not be quite as efficient at diluting waste as a single large waterchange, if you don't mind using a little more water you can maintain a far more consistant and lower nitrate level than is possible by relying on large weekly water changes, and with a large heavily stocked tank that is when they are relly worth their while.

To me auto Wc isnt a good method

As above, depends how it is set up and how much value you put on your time. You could have a fully automated system like Henwards where there is no need to ever do water changes, or a semi-automated system where you drain it first then refil, or something in between. My next big tank will have an automated system, not a continuious drip but one that does something like 10% daily in one hit. IMO the increase in water use is made up for many times over by the time saved, the decreased stress on the fish and the improved water conditions.

[Jaxxnz]

depends on how u set it up

ive got mine so it drains first then it fills

but then you have to turn off you sump pump??

[GrahamC]

The two siphons most commonly used in aquaponics for automated water changes are the bell siphon, and the loop siphon. The loop siphon can be easily modified to do a partial water change, but I'm not clear if a bell siphon can do this with 100% reliability. You would need a siphon break, and that would be the issue .. you certainly don't want the whole tank emptying!

[R32GOTMLK]

but then you have to turn off you sump pump??

wouldnt have a clue im running externals on my tanks

[GrahamC]

My next big tank will have an automated system, not a continuious drip but one that does something like 10% daily in one hit. IMO the increase in water use is made up for many times over by the time saved, the decreased stress on the fish and the improved water conditions.

Luckily many of us don't live where water usage is metered

[Jaxxnz]

David are you think of my WC toilet cristern method..one flush can withdraw the amount you desire.. :slfg:

[Squirt]

@Henward

Back to your issue, ill crunch some number for you.

Let's just say your tank is 2100L and it changes that every week so 300L a day. So 14% per day

Day 1

14% water change 86% old 14% new

Day 2

14% water change 73.96% old 26.04% new (since the start of the week)

Day 3

14% water change 63.61% old 36.39% new " "

Day 4

14% water change 54.7% old 45.3% new " "

Day 5

14% water change 47.04% old 52.96% new " "

Day 6

14% water change 40.45% old 59.55 new " "

Day 7

14% water change 34.79% old 65.21% new " "

In theory your only done 65.21% over one week. But if all your water change where done at one a 98% water change.

[GrahamC]

It may be more effective at diluting waste on paper, but you have to take into consideration the fact that an aquarium will have ever-increasing nitrate levels. Draw a line graph showing nitrate levels over time and compare the increase/decrease while doing 100% changes every two weeks, 50% changes every week, 7.14% daily change and 0.3% hourly change you will see that although the larger less frequent changes are more effective at reducing the nitrates, if you're changing the same amount of water in larger less frequent lots the nitrate levels will get higher between changes than they would with smaller more frequent changes.

It doesn't matter what system you use. If you remove less nitrate than is created, you'll get nitrate creep.

[alanmin4304]

In most cases nitrate is not a problem and in my view the consistant conditions created by an automated water change system are a big advantage. Most problems are caused by rapid and large changes to water chemistry so you need to do very regular and reasonably sized water changes to avoid that.