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You have a good start. I would do a larger cluster in the rear leftish corner of the tank with some rocks pointing up to give it some height and a smaller cluster in the front right side with again smaller rocks pointing up.
I like the last picture the best but I'd still move some of them.
The one all the way to the right I don't care for. I love the one standing up but maybe move it a little to the right. The big one on the left hmm I think may be to big idk.