Calcium for shrimps

Shrimps need calcium, everyone knows that. They need more calcium because it's the main ingredient in their shell. This is why a lot of shrimp food is advertised as calcium rich.

A few things I gathered from various source, all may not apply but this is what I currently believe in.

What you should avoid or be cautious,
- Too high a GH in water (mainly calcium) is actually bad for shrimp, it will cause molting issue. One theory is that their shell grows so well it's too hard to molt.
- Too low a GH makes molting easier, however, it may also cause issue with shell development.
- Spinach contains high calcium, however, the oxalic acid (草酸) and Fe in spinach are calcium blockers -- they reduce the ability for shrimp to absorb and use the calcium.


What you can do to help calcium intake,
- Vitamin D helps calcium intake. I'm not sure high light helps but researches have been done and prove that longer photo period increases shrimp growth. Here is an interesting paper (http://ntour.ntou.edu.tw/ir/handle/987654321/10676)
- Other vegetables may actually be better for calcium supplement - bok choy, broccoli, cabbage ... etc.


Some other things I have found, tried, or thinking of trying:


Cuttlebone: it's vouched  by a lot of shrimp keeper for its benefit to help molting. Since it's cheap and seem harmless, I use it too. But you should know that,
- It does increase the GH/TDS. I added one whole cuttlebone (cut into three pieces) in 500ml of water of TDS 175. After 48 hours, the TDS got to almost 600.
- However, I put one section (1/3 of a whole cuttlebone) into a 6 gallon tank. After 24 hours, there was NO TDS increase.
My conclusion: while it does increase TDS, small amount doesn't have noticeable effect.

BW minerock: I have it in one of my tanks, not sure if it is effective or not. No noticeable difference in that particular tank. It may have increased the molting frequency but I'm not sure if it is due to this. Since I bought some, I use it.

There are lot of other products but hard to get. When I get something new I'll add my experience here.