I have been in the reef hobby for 17 years and for monetary reasons I am forced to go back to freshwater.
I have some basic questions, anybody willing to help?

post up, what kind of fresh water tank do you want? planted, fish only?

It will be a 180 gallon Oscar tank. I will not want any live plants as the reason I am leaving reef tanks is the intense lighting.
My main questions are substrate and water movement.
What would be my best choice for substrate and will I need to keep my big circulation pumps for water movement?

For a fish only tank use whatever substrate you feel like, I have always used pea gravel from my backyard. Just keep it thin enough that you can vacuum it all. I like some water movement in all my tanks but you only need about 1/10 what your reef had. Are you using your sump as your filter? Remember you will not have all of your live rock/live sand for bio filtration any more.

You don't need reef lighting or anything near that level to have live plants.


plus the plants will make the operation balanced out and stable.

Just like algae in a reef tank (refugium) does.

my .02

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fw leiden since 1979, fo salt since 1979, mixed reef 55g 2002-2009. Strong emphasis on the tank taking care of itself. Balanced with plant life, no water changes, tap water, no filters in FW. Only dosing calcium, alk, mag in marine reef tanks. http://www.aquariumforum.com/f15/my-...ods-26410.html
recent tanks (till 2009) 7 years- 10g FW leiden 7 yrs, 55g mixed reef 7, 2 yrs, 20g FW leiden, 10 g fw leiden , 29g mixed reef, current tank 55g leiden

Just FYI I have a 75 gallon tank that has a standard 48 inch perfecto light with a single 32 watt bulb. I have anubias, java fern, and a large amazon sword. The sword could use a little more light but the others are thriving. I am not sure how oscars do with live plants, Ive never had those two together.

Won't Oscars wreak havoc with live plants?

I think they might.

In which case you setup an external or in tank refugium to keep the plants away from the oscars.

Just a partition so you have a fish area and a plant area would be sufficient.

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fw leiden since 1979, fo salt since 1979, mixed reef 55g 2002-2009. Strong emphasis on the tank taking care of itself. Balanced with plant life, no water changes, tap water, no filters in FW. Only dosing calcium, alk, mag in marine reef tanks. http://www.aquariumforum.com/f15/my-...ods-26410.html
recent tanks (till 2009) 7 years- 10g FW leiden 7 yrs, 55g mixed reef 7, 2 yrs, 20g FW leiden, 10 g fw leiden , 29g mixed reef, current tank 55g leiden

Thanks for the idea but I think I will probably just go with fake plants and driftwood to keep the cost and maintenance to a minimum.
Unfortunately my budget is substantially smaller now or I would not be giving up my reef "habit".

I use a thin layer of gravel, sand whatever (if any substrate at all!) and just use potted plants. I know oscars like to dig up plants and what not, but I don't think they eat them?

I don't know if they will eat the plants but my oscars regularly re arange the tank and they are pretty strong, so I doubt there are plants that would stand up to a rambuncious oscar.