I don't think it will cause a problem, that is quite a low level.Marine fish can tolerate 80-100 nitrate (not that you should leave it at the level if it got that high). I would test for ammonia and nitrite to be safe. If they are zero then use it, nitrat after all is the safer end product of the cycle.
Hey Tarek,WELCOME TO THE SITE BY THE WAY. what sort of set up are you doing? can you give us some more info so we know how to advise you for the best. Eg are you haveing a fish only set up, reef only or both. Whats size tank and what equipment, rock, lights etc you will use?
Hi, My tank is 350 litres and I am going to start with a fish only system with a small amount of live rock and go from there. I have installed a t5 luminaire for future use and to spur on the live rock and I have 2 external filters which are set up pretty much as mechanical filters with one attached to a uv. I've also added 2 small powerheads for circulation and a protein skimmer which I can't get to work (as you know). I will add the live rock once the tank has been running a couple of weeks and all I have in their at the moment is a substrate of live sand which I hope will start things off. I used to breed discus and thought I knew alot about fishkeeping but I am in the process of being rudely awoken.
It will be easier to add more live rock at the start up stage rather than to add it later when you have fish. You will find it will then cycle and add ammonia to your tank all over again, affecting your stock. If you add more rock now, it will avoid all that and the tank can cycle once, settle down and be ready in 3-4 weeks from now(if lucky) to add whatever fish you want. It is easier said than done adding it once a tank is established.I know it is costly but it will be worth getting it al how you want it first, then add stock...just a tip..
The normal recommendation is 1kg of live rock per gallon of water.I haven't got as much as that I know. That amount is more applicable if you are using your live rock as the main filtration system in your tank (to know more about this you can read up on the Berlin method). I have a good amount of live rock in our tank but it is mixed in with ocean rock to bulk it out. In the end it will become a type of living rock, but it takes a long long time for that to happen.I too, have external filters so I am not using live rock as my main source of filtration, so you won't need the full amount either. Get as much as possible though it is best to have more than not enough. It also grows coraline algae and other marine creatures come with it.I did an article on setting up a marine tank - see the article section. It shows a photo of when we added the live rock. The live rock is the darker rock in the photo the light rock is the cheaper ocean rock.