how frequently change water

I had a hard time identifying some of the plants. I included one of my anubias nana which I hope won't melt under the intense light.

I think the plant pictured below might be a java fern but I'm not sure.

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I remember changing my water once a long time ago, It was messy dont think Im going to do it again for a while.
 
I had a hard time identifying some of the plants. I included one of my anubias nana which I hope won't melt under the intense light.

I think the plant pictured below might be a java fern but I'm not sure.

Looks like a crypt. The Java fern is the far left biggest plant.
 
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