You could always order one more facing up for agitation on the surface and the other could be faced in to the rock build.
I bought this one http/cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=370261878330
thinking my 3000l/h would be too much flow and people was recommending to order 2 of them, I thought with it being 2000l/h one will be enough but when it came it was tiny compared to my 3000l/h and it looked like it was only doing 1000l/h.
I don't know if the size of the power head affects how efficiently it runs but I would just wait until it arrives and see how it handles. I really do like the scaping you have done with the rocks so I'm not telling you to take more rock out but with so much in there I'm sure that the Koralia 900 by itself wouldn't make enough turnover in the tank.
Every saltwater setup using live rock needs at least 20x turnover at a minimum. They way you work it out:
e.g. Powerhead flow rate (900l/h) ÷ tank volume (50lt) = (18x turnover)
I bought this one http/cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=370261878330
thinking my 3000l/h would be too much flow and people was recommending to order 2 of them, I thought with it being 2000l/h one will be enough but when it came it was tiny compared to my 3000l/h and it looked like it was only doing 1000l/h.
I don't know if the size of the power head affects how efficiently it runs but I would just wait until it arrives and see how it handles. I really do like the scaping you have done with the rocks so I'm not telling you to take more rock out but with so much in there I'm sure that the Koralia 900 by itself wouldn't make enough turnover in the tank.
Every saltwater setup using live rock needs at least 20x turnover at a minimum. They way you work it out:
e.g. Powerhead flow rate (900l/h) ÷ tank volume (50lt) = (18x turnover)