Converting From Freshwater To Marine

[pops1981]

Hi guys,

I have been cycling (fishless) a freshwater tank for about 3 weeks now. Following a visit to a new lfs i discovered, i have changed my mind and would like to go the marine route. I have a number of questions that i would like to ask:
I intend on keeping only fish (with possibly live rock). Probably no more than 3 fish, one of these being a clown.
Is live rock a must?
1) I have a 90ltr tank, which currently has coral gravel, ocean rock, a fluval 4 filter, and a heater. Would this be ok?
2) Can i do without a skimmer. If i was to forego a skimmer, what work would be involved in maintaining a safe environment? ie water changes etc.
3) Can i keep the fluval 4 filter, it is also pretty powerful and creates a good current within the tank.
4) If i am only keeping live rock and fish are there any special lighting requirements.
5) As my tank has already been cycling, the condition of thew water for freshwater fish is perfect, thus i assume that the correct bacteria are present for this. Are the bacteria for saltwater completely different. Or is it a case of just replacing the water with saltwater and cycling the tank again.

Many thanks for your help.

 

[Anguilla82]

I intend on keeping only fish (with possibly live rock). Probably no more than 3 fish, one of these being a clown.
Is live rock a must?
Using Live Rock as the main filtration is currently the way that most people filter their system and is a very natural way of doing so. so IMO, yes.

1) I have a 90ltr tank, which currently has coral gravel, ocean rock, a fluval 4 filter, and a heater. Would this be ok?
Yes but stocking would need to be light, around 4 small fish would be right.

2) Can i do without a skimmer. If i was to forego a skimmer, what work would be involved in maintaining a safe environment? ie water changes etc.
With a tank your size you can easilt do without a skimmer. Regular (i.e. weekly) water changes would remove any build up of nitrates.

3) Can i keep the fluval 4 filter, it is also pretty powerful and creates a good current within the tank.
Is this an internal or external filter? If internal i'd replace it with a dedicated powerhead (look at the Koralia Nano for instance). If it is an external you could use it as a place to put extra live rock, add a bit to the overall system litreage, and use it as a place to put phosphate removing media (e.g. rowaphos).

4) If i am only keeping live rock and fish are there any special lighting requirements.
No

5) As my tank has already been cycling, the condition of thew water for freshwater fish is perfect, thus i assume that the correct bacteria are present for this. Are the bacteria for saltwater completely different. Or is it a case of just replacing the water with saltwater and cycling the tank again.
Unfortunately the bacteria in saltwater are a completely different strain to those in freshwater, and the ones in your tank now would mostly likely die when you increase the salinity of the water. You're going to need to strip the tank down and start the cycling process again with salt water.

 

[TigerIssey]

As Rob says, about 4 fish would be fine. I would make that extra one a second clownfish. They are amazing to watch as pairs, if you buy 2 juvenile, they will both become males then the dominant one will grow bigger and be the female.

 

[pops1981]

Thanks for your replies.

With regards to filtration, my current filter is an internal one. If i was going the fish only route could i still use this one if i started again and cycled for saltwater?
From what i read a powerhead will create enough current in the tank to flush the matrial through the live rock, which in turn will filter the tank? am i correct in my thinking?

So my two options would be either a fish only tank (in this case how would i filter)?
or a Fish only with Live rock, in which case i would replace the filter with powerheads?
or what would be the implications of running a fish only tank then slowly adding small amounts of live rock.

Thanks again

 

[jtnova13]

With fish only, you could probably use a HOB (hang on back) filter or canister, but you'd have to be very meticulous in cleaning it so it doesn't become a nitrate factory.

You could add LR slowly as long as it is cured, but I believe you'd need T5 lighting, whereas FO requires less.

 

[SkiFletch]

You can definitely add LR slowly over time to a FO system with a mature filter. The biggest difficulty is the possibility of algae blooms when introducing LR to what will likely be a nutrient-rich FO system