I was given a 125 gallon tank. It was salt water. I was told I would need a sump but it is not drilled. A friend of mine has a tank that runs 2 large canister filters, no sump. Is it possible to run a larger saltwater tank on just canister filters?
You don’t need a sump. I wouldn’t use canisters they are poor choices for salt water. You can run it with hang on the back filters. They are much better for SW. in a well balanced properly stocked SW tank you don't really need need a filter. The live rock provides the filtration. I have a 120 with a sump but in reality the sump is just a place to hide my protein skimmer. All the filtration is from the live rock in the tank and some smaller pieces in the sump. You can get a hang on the back protein skimmer if you like.
IMHO canister filters are not the best but still effective.
I recommend you start the system with macro algae right from the start. that way the system will be balanced and stabilized from the get go.
Macros do best in a refugium which in its' simplist form can just be an in tank partition.
You can build an HOB drain to a sum with $20 worth of PVC. And it will be just as reliable as any drilled setup.
If you do go sump:
1: test power out to insure no floods.
2: test normal operation returns when the power returns.
3: test there is no flood with drain failure. (blockage, siphon break). The sump should run out of water before the display floods.
I ran canisters on an old 55g tank for a while and felt they did a pretty good job. I ran 2 canisters though so that I could alternate the cleanings every other week or so as to avoid I killing off too much biological filtration at a time.
I would always recommend sumps/refugiums for a reef thank though whenever possible. Doesnt mean u cant have a successful reef, all systems have their pro's and con's. Sumps just tend to have more pro's.