# Marine Aquariums > Saltwater Beginner's >  a couple of questions about water

## lost

First one is in my 68l tank i have two power heads rated at 200l ph is this going to be enough?Secondly at the mo the sg of my water is 1.25 i am thinking of getting some ready mixed ro water from my lfs and doing about a 10% water change i no i dont have much in there at the mo but will the difference in the sg be ok?Lastly not sure if this is the right place to ask this but i did read if my shrimp is stressed ie water quality it wiil molt more often and if it moults a lot it may not live as long ???

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## Timo

Flow depends on what you are keeping. Your flow is about x6 per hour. Different depending what you keep SPS need x15-25 per hour, fish and softies around x5-15, as long as the flow is laminar and not stream general more the better. 

Salt levels also depend on what you plan keeping SPS higher around 1.025 (33) but fish only system do much better at a lower level around 1.019 (26). Different tanks use different levels and not one rule works for all as most tanks are different.

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## lost

Thanks Timo so by the sounds of it,it wouldnt do any harm if i had more flow in there.As i have said before because the tank is deep insted of long it dose look as if there is a lot of flow in there

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## Timo

It does depend on the tank size as well, maybe you could lower one if the surface is too wavy.

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