Hi,
personally I have never experienced any problems with water change. Linkei are really tolerant with such disturbment. They are only very vulnerable regarding the parameters of the water, especially temperature. If the water is too cold they will stand still and behave almost “shocked frozen”. Mine could after such an event luckily recover quite well. This is also true for eggs and/or fry! They will not like a “shower of fresh water through their cave but as long as you keep the nest out of direct water movement, everything is alright!
I think that the most important thing with keeping fish is waterchange no matter what species and i always change at least 50% of the water every week. I am convinced that this is a very essential point because of simple mathematics:
There is a constant flow of pollution into the tank from food, debris and the fish’s metabolism. These accumulate during a waterchange period and are then partially removed. The important word here is partially: If before your water change you have, say 1 gramm of pollutant xy in the tank, you will remove only a fraction wich is in line with the fraction of the whole volume you remove. So if you then change 20% of the water you will end up with 0.8gramms after the waterchange. However, in the consecutive period there will be another 1 gramm added to give a total of 1.8 gramms of which you then take out another 20% which leads to 1.44 gramms and so on…
week 3: 1.952g
w 4: 2.3616g
w 5: 2.689g
w 10 3.57g
From about week 16 we are getting close to the upper limit where there is no more significant increase of pollutant xy. Its about 4 gramms. This is huge since when compared, we find that it is the same as if we had not done any waterchange for 4 weeks!!!
Now this is surprising and should be alarming. but what if we do the same for another amount of waterchange?
Say again, 1 gramm of pollutant xy is added but we do 60% Waterchanges:
week 1: 0.6g
week 2: 0.96
w 3: 1.176g
w 4: 1.3056g
w 11:1.46g
w 30: 1.499999668g
Seems like we have a limes (limit which is never reached) here again! But what surprise: its only about 1.5 gramms!!!
now what about 50% waterchange?
w1: 0.5
w2: 0.75
w3: 0.875
w4: 0.9375
w5: 0.96875
w6: 0.984375
and so on… limes: about 1 so we end up with the constant amount of 1 gramm pollutant xy.
seems cool, right? By simply increasing the amount of water we exchange, we can have significantly better results!!! and they are sooner reached so there is a lot less time in which the amount is strongly changing -> our fish can get ued to it sooner! what if we really go for it and do 70% waterchange?
w1: 0.3
w2: 0.39
w3: 0.417
w4: 0.425
w5: 0.42753
w10: 0.4285688979
WOW within only 4 weeks to a constant rate of about 0.43 gramms!!!
This has to do a lot with mathematics and numerical sequences. In facht, if you have “real data” of any kind, you can run the calculation yourself with any a bit more sophisticcated smartphone-calculator app or with old-school calculaters. Even my Texas Instruments-30 worked well here 🙂
The equation is:
an=(an-1+c)*q
with:
an: the amount of substance xy after n weeks/periods
an-1: the amount of the previous week
c: constant net inflow of substance xy (in the uper examples it was 1 gramm that came in every week) within the period
q: the fraction of the water that remains IN the tank (in my first example it was 0.8 since 80% of the water remained there) so it equals 1-the percentage you are changing.
Actually, you can also use it if you want to calculate how much fertilizer etc. your plants need to keep a certain level of plant nutrients.
Now this has gotten very long. I hope you are not bored but I think it is best to show with examples why I do the waterchanges the way I do them: 50% because the whole total will never get above the amount that would be added within 2 weeks which I find an acceptable thing.
Of course this is not a very sophisticated model of the Aquaria but it might give a reasonable idea of how we should choode our Waterchange-ratios.