Data given by PUB -
http://www.pub.gov.sg/general/Pages/WaterTreatment.aspx
"On Monday, my tap water ph reading is 8.2, on friday, its 7.3!"
"On a water change on monday the chloride level in the tank seems alright, on another day its seems to have a strong chlorine odour."
"Breeding or raising discus is not as easy as what it used to be!"
The above are some comments I heard from few discus hobbyists who change their tank water 100% daily.
I guess not only discus suffered, other aquatic fishes or shrimps do suffered if a large water change were to be practised. As a matter of fact I often practised 80-90% of tap water change for shrimp setups. However that was about a year or two ago when Im dosing chemicals like formalin, methylene blue, bifuran, etc and even anitbiotics like tetracycline. And if theres any chance of me doing that again with the current tap water. The answer is a definte NO. Reason being I have lost too much shrimps due to heavy water change. Shrimps are small and unlike fishes who are able to show symtoms if they are sick or under bacteria attack. Even so, exact medicine availble for treatment is not readily available at present. Therefore to judge whether they are alright after a major water change is difficult for anyone.
So I do recommend shrimp hobbyist in Singapore do play cautious when comes to water change and to prevent disease-prone shrimps, purchase shrimps from reliable sources. Right now I only top up my CRS tank with distilled water. Those tanks with high nitrates, i do try praticse a 10% water change each week or if budget allow i will shop to add more cannister filters.
Cheers.