我先来介绍一下自来水中对鱼类有害的一些主要成分和去除方法。首先，自来水中的氯气需要静置2—3天，或燥晒1天（如果急用可按每100kg水加入0.63克大苏打，即硫代酸钠即可立刻使用）。其次，氯胺虽然文章不常提到，但也是养好鱼的关键问题之一。有些地区的水质中有较高浓度的可溶有机物，如果这时水厂直接加入氯气，就可以与这些有机物结合形成一些致癌物质，对产生危害。因此，水公司在水中同时加入氯气和氨气，这两种物质可以结合成一种新的物质叫氯胺，而氯胺不与水中的有机物结合，所以当除掉水中的氯气后氨还是在水中，这需要一个良好的氮循环，既利用生物过滤可以去除。

此外，PH值也非常重要。如果想增加PH值，可以使用碳酸氢钠（小苏打），而如果想降低PH值，则应使用磷酸二hydrogen钠。注意，同时使用PH试纸，每天调节PH值的度不要超过0.5。但是你要知道，0.5对于鱼来说相当于water里的酸或碱增加了50倍……最后提一下：不断为water充氧也可以起到稳定PH值的作用。

再谈适当的鱼数量，你可能会问，这和water有什么关系？回答是当然有的，而且关系很大！fish越多排出的废物越多，污染、疾病、死亡随之而来……基本原则是平均10升water养的fish总长度不超过5.5cm（注意:体长标准是从鼻到身体末端距离，不包括尾巴）。

至于nitrogen循环的情况，我要指出的是，只要put fish in the tank，它们就会排出ammonia and other waste into the water, water's ammonia concentration will rise, then some beneficial bacteria will decompose ammonia in the water, but this process needs a week or longer to form these beneficial bacteria groups during which time fish suffer greatly.

However, things are not that simple because these beneficial bacteria only convert ammonia into nitrite salt but still toxic to fish! So when ammonia concentration decreases while nitrite salt concentration rises, another type of beneficial bacteria forms groups and converts nitrite salts into relatively harmless substances called nitrates controlled by regular water changes.

The entire process from ammonia to nitrites and finally nitrates is called nitrogen cycling cycle which requires 2-3 weeks to achieve a good nitrogen cycle state for a new aquarium.

If your biological filter has not yet formed and your fish appear problems you urgently need to handle the water quality:

For Ammonia:

Change part of the water (lowering concentrations)

Add activated alumina (absorbing Ammonia) inside filters

Add helpful microorganisms

For Nitrites:

1.Change Water

2.Add table salt (although cannot reduce it but can neutralize toxins)