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Thanks, HH! Interesting. Things are invariably more complex than we see them, even having done them thousands of times.

If I understand the study correctly,
angels were housed in 500 liter tanks, with 10 l per fish, that is, in groups of 50. Fish were 30 to 55 mm long, that is, sexually immature. BUT 10 l-a fish is not much room for 5 cm angels.
Than groups of 34 fishes are formed, but unfortunately, the size of the housing is not mentioned.
After 4 days water is changed 0 % 25 % of 50 % and aggression is measured. As in each case 50 5 of the water was removed, but in the 0 % group it was returned, any found difference cannot be ascribed to mechanical differences
Still, fish are chemically very sensitive, and cichlids perhaps even more. I can imagine that after being given 50 % clean water, the fishes do not recognize each other by smell anymore. That is, it could well be that the 50 % water change group has had its social structure cancelled.
An other option can be that the water was somewhat polluted, and cichlids tend to be less active in polluted water. Changing 50 % made the water clean again, resulting in normal levels of aggression.
What I would be interested in is - would it be better to change 10 % a day, or 50 % a week. Unfortunately, this is not tried to be ansewered.

Hi all,

Bas Pels wrote: ↑17 Oct 2017, 20:28 ...... An other option can be that the water was somewhat polluted, and cichlids tend to be less active in polluted water. Changing 50 % made the water clean again, resulting in normal levels of aggression.
What I would be interested in is - would it be better to change 10 % a day, or 50 % a week. Unfortunately, this is not tried to be ansewered.

I would have to agree with @Bas Pels, there are a number of factors in the experimental design that make it very difficult to draw any conclusions about why the water changes effected behaviour, or even whether they really did.

cheers Darrel

For most tropical fishes large swings between poor and good water conditions signal the onset of spawning season. This means time to get aggressive to secure a mate.
-Shane

Shane wrote: ↑19 Oct 2017, 02:10 For most tropical fishes large swings between poor and good water conditions signal the onset of spawning season. This means time to get aggressive to secure a mate.
-Shane

Agreed.

Bas Pels wrote: ↑17 Oct 2017, 20:28 What I would be interested in is - would it be better to change 10 % a day, or 50 % a week. Unfortunately, this is not tried to be ansewered.

You won't get the same result in chemical concentration because the amount of chemicals/ contaminants will be higher in a 50 percent change than respectively in a 10 percent change.

troi wrote: ↑01 Nov 2017, 22:19

Bas Pels wrote: ↑17 Oct 2017, 20:28 What I would be interested in is - would it be better to change 10 % a day, or 50 % a week. Unfortunately, this is not tried to be ansewered.

You won't get the same result in chemical concentration because the amount of chemicals/ contaminants will be higher in a 50 percent change than respectively in a 10 percent change.

I ran the math on this. Both systems hit equilibrium points under any set of conditions I assumed. Equilibrium on the 10% change every day was very stable. Equilibrium under the 50% change once a week was a repeating cycle which ranged from lower than the 10% model (just after the change) to higher (just before the change).

Overall benefit to the fish probably depends on questions of acute versus chronic toxicity. However, the 10% change will probably mimic a larger body of water better.

Without any math, it is easy to explain why virtually all systems with a stable waterchange protocol reach an equilibrium. The only condition is, that enough water is changed: changing 1 percent a month will not suffice.

Assuming the water is mixed will when changing, a 50 % change will remove 50 % of all waste in a tank. So, if the water is initially clean, and after a week 1 gram of waste is produced, half a gram is left behind.

The next week will produce again a gram, the whole is 1.5 grams, and 0.75 grams is removed. Leaving 0.75 grams behind.

This will gradually increase untill the concentration before changing has reached 2 grams. 1 will be removed, leaving 1 gram, and by the next time thew concentration is back to 2 grams.

If I were to repeat this with 10 % a day, and producing 1/7 th of a gram in a day, equilibrium would be at 10/7th of a gram.

In each equilibrium the exact same amount of waste is removed as is produced since the last waterchange

The value at equilibrium is also predictable: if one removes 1/x of the water each time, equilibrium will be x times the production of waste in the time beween waterchanges.

Obviously, normally noone knows how much is produced - but the water quality is easily measured

Hi all,

Bas Pels wrote: ↑02 Nov 2017, 07:48.......The value at equilibrium is also predictable: if one removes 1/x of the water each time, equilibrium will be x times the production of waste in the time beween waterchanges.

Obviously, normally noone knows how much is produced - but the water quality is easily measured

It doesn't tell you what ions you have, and every-one will have a different datum value (dependent upon the hardness of your water), but you can use a conductivity meter to monitor the changes in water chemistry over time. Conductivity meters are both accurate and "plug and play".

Ideally you get a datum value when you first fill the tank, for me it is about 80 microS (~50 ppm TDS) which is the average conductivity of the rain-water I use (this is a limestone area).

Once the tank is established (and your water change regime is in place, ~10% a day for me) you measure the conductivity again, and then you monitor it over time. As long as the fish are in good condition you just carry on the same.

I have lightly stocked, heavily planted tanks run the tanks at between 80 - 140 microS, if I'm away when I come back I change proportionately more water every day (but never more than 20%) until I'm back in the 80 - 140 microS zone.

In the winter the conductivity of the rain-water declines and if I get below the 80 microS value I use a small amount of our tap water (about 18dKH) added to the water changes.

cheers Darrel

You´re copmpletely right Darrel - if you know your system, conductivity can tell you wheter the waterneeds changing or not.

It´s not the value that counts, but having your watergone from 80 to 140 - that´s what is important. Because you know 140 is high.

That´s also the problem with using conductivity: as long as the system is not yet known, the numbers - whether 7, 77, or 700 will not have a meaning. And thus, when something changes, such as the source of the tap water, you will have to start all over again.

I happen to live between two wells, and sometime my tapwater comes from one, sometimes from the other. They are measurably distinct. Therefore, this system does not work for me

Hi all,

Bas Pels wrote: ↑02 Nov 2017, 20:20 You´re copmpletely right Darrel - if you know your system, conductivity can tell you wheter the waterneeds changing or not.

It´s not the value that counts, but having your watergone from 80 to 140 - that´s what is important. Because you know 140 is high.

That´s also the problem with using conductivity: as long as the system is not yet known, the numbers - whether 7, 77, or 700 will not have a meaning. And thus, when something changes, such as the source of the tap water, you will have to start all over again.

I happen to live between two wells, and sometime my tapwater comes from one, sometimes from the other. They are measurably distinct. Therefore, this system does not work for me

Yes, the datum value is the problem.

I'm lucky that our tap water (Corsham, Wilts <https://en.wikipedia.org/wiki/Corsham>) comes from a deep limestone aquifer and is pretty consistent, very low in NO3, with a small amount of sodium (Na), plenty of calcium and bicarbonate (18dKH) and not much else.

If I kept hard water fish in our tap water 600 microS. would be my starting point (datum value).

The conductivity of the rain-water goes up and down through the year, minimum of about ~30 microS. in the winter, maximum of ~140 microS. in the late summer when they are cutting the corn and there is a lot of dust.

I have access to DI water as well, but I haven't used it recently (we haven't had any prolonged spells of dry weather, when the conductivity of the rain-water will rise and I can't keep below the 140microS. value using it, or I run out of rain-water because of drought or prolonged freeze).

cheers Darrel