如何可以keep個ph值constant?

To give different pH, just add an acid.

But if you want to keep the pH constant, surely only relatively,
buffer is needed.
Buffer is a system which contain
a weak acid and it's conjugated base in a comparible amount.
It can be prepared by mixing the acid with a salt of it.
A rough calculation is pH = pKa - log([salt]/[acid])
(pKa is easily found in the Wiki when search for the acid)

However, there is a difficulty is that how could you confirm
that the buffer or acid do not affect the normal srimps' growth.

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Sor, 因為打完先發覺原來你係用中文問既...

我既suggestion係用buffer
o者係一隻弱酸加佢既鹽, 兩者份量不大差距就得
pH = pKa - log([salt]/[acid])

當然最有效既方法梗係用無限大既pH溶液 :P
因為buffer都有capacity.
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最後你要carry out in fair我的確答唔到...
我既唯一想法就係keep無隻蝦既solution都always有齊D acids.
不過都係個句, 點知acid本身會唔會影響隻蝦呢 = ="