Ok im starting a reef tank, but i have the fluval osaka 70 gallon so a sump wasnt really a option. Im just kind of worried, using a decent hang-on skimmer will i be ok? or is it going to be a lot more work for me to do this.
You should be fine. Things like heaters (if needed) can go in the tank itself, and as long as there's enough flow from powerheads and live rock for filtration, there's no reason you can't have a healthy tank without a sump - just have to stick to a regular cleaning schedule, same as if you had a sump
Main benefits of sump is to add more water volume (more of a benefit for smaller tanks, imo), keep more things out of the main tank (heaters, skimmer, etc.) and for things like auto top off, calc reactor or whatever else they might to set up. There are workarounds for most if not all of those without using a sump though, so as you discover additional tank needs, you should be able figure out how to make it work
One other thing to note is that many people like to keep chaeto algae in the fuge section of their sump for nutrient exportation (keeps nuisance algae down in the display tank) - for this there are HOB fuge options as well (people have modified AC filters to make their own or you could just buy ones from CPR)
I have a fluval 405 should i put some stuff in that? for extra filtration? Right now i just have the stuff in it that it came with, someone else before mentioned putting some live rock in it or something???
I used to run a 32 gallon bowfront sumpless.
It was heavily stocked and my first non all in one (biocube/aquapod) salt water aquarium.
The osakas make gorgeous reefs, I run a 95 gallon seamless bowfront myself though so maybe I'm biased.
The Fluval is essentially a sump in many ways, it adds a little water volume and you can hide various additives to it.
I modded a rena xp1 that I drilled a hole in and put the heater in there and siliconed around the hole to hide my heater.
You can definitey run live rock in there as well, rubble is best to provide the most surface area possible for your bacteria.
Carbon is also a great additive to run in there, but you will need to change it regularily as well as clean the canister itself at least monthly.
Buy the best HOB simmer you can afford, Deltec makes some of the best ones out there, this alone will negate any major non cosmetic advantages of having a sump.
There is an excellent chance you can run some of that in your 405 as long as they are getting agitated enough to allow them to work...
running these would be better than live rock rubble and carbon combined IMO.
I definitely wouldn't run it with the normal filter media (they become nitrate factories as others have mentioned) - you could run it with live rock in there, but it could still require a lot of cleaning (I've never used the Fluval 405 so not sure if there'd be any deadspots or detrius build up in there)
Personally, I would just keep trying to find a buyer for that and use the funds to add to your SW budget
You can use the 405 for additional water flow or for carbon filtration.
If you have enough live rock you are not going to need additional bio filtration.
Don't use too much live rock either.
Alot of people put too much in their tanks and pile it up against the back of the tank like a brick wall.
That just traps a lot of detritus and leads to algea problems.
You want to minimize the amount of contract area with the bottom of the tank and the rocks.
Stack it openly so water can flow through, around and behind it.
yeah I have it all in the middle of the tank so there can be flow around the outside of the rocks, i still have to get the glue or whatever so i can put it together so it doesnt fall over or anything. Im really enjoying it so far even tho all i have is live rock and a couple of fish!