Fresh v salt: cycling saltwater through a freshwater external filter

[Lynnzer]

Briefly - I have made a start on going into a marine tank. I have bought a good number of rocks, not live, though some will have a small amount of "life" in them as I hung them into the sea for a fortnight.
I have these in a small tank with shop bought saltwater to condition them. I am using an external canister filter that I took from a running freshwater tank, replaced all the freshwater with saltwater and left all the filtration pads, bio-balls and ceramic rings untouched, so presumably the bacteria would just "hop across" to the new marine environment. The bacteria is supposedly the same for both environments.
1st of all, is this a true expectation.
2nd, since I set this all going around 10 days ago, the ammonia, nitrite and nitrate levels have been off the scale and show no signs of going down. I have added a quickstart solution in generous amounts with no difference. I wonder if this is wrong too.
I plan on emptying my 130 ltr freshwater tank today and making the transformation to saltwater as quickly as possible but I need to be sure that I'm not going to kill everything that goes in.

I plan on using, and have already made, an internal sump filtration system with a DIY protein skimmer

Any useful advice on what I'm doing wrong, what I need to do to get the water parameters correct in a fishless tank would be great.

 

[Uberhoust]

No advice but will watch this thread. I live near the coast and have thought of establishing a saltwater tank with native fish.

I have heard the same about the bacteria, I think the genus might be the same but not the species. I have a hard time believing that bacteria grown in fresh water will do well in salt water, I would expect them to all dry up due to the change in the osmotic pressure. This thought is not based on any research.

 

[Lynnzer]

So far, the external canister filter tank, flushed out and filled with saltwater in a tank with lots of rocks, indicated extremely high amonia, nitrite and nitrate levels. I added a large amount of live marine bacteria and left things as they were except for a small amount of flake food.
Things didn't change much until a couple of days ago when the parameters were all ideal. No traces of the dreaded 3 chemicals.
So, just to test things out I acclimated a black molly over the course of a day to saltwater and added it to the tank. It's doing fine. In fact it appeared to have a small nfection on 1 eye in the freshwater tank so I expect the salt will clear that easily.

The time to carry out the nitrogen cycle has been very quick. I put this down to the amount of nitrifying bacteria introduced in the tank.

 

[Lynnzer]

Things are just dandy. I ran out of NT Labs ammonia test fuid but the nitrite and nitrate are still at zero. Instead of buying more ammonia bottles of fluids I opted for a Seachem Ammonia alert round strip thingy. It lasts a year and is a lot less expensive then buyin the NT Labs bottles.
I have added more fish and sps corals and am calling it a day on the tank. I won't be adding any more livestock, except perhaps more coral.
So the inhabitants right now are 2 common clownfish, a mandarin, a Red Head Fairy Wrasse, a blue streak cleaner wrasse, a Yellowtail damsel, 1 Flame Shrimp, and a couple of snails and a hermit crab.
Everything's running well. I have bought a pair of Kessil Tuna Blue A160WE with a controller so am currently deciding on the timings and intensities for the lights.
I have in mind reshaping the live rocks as more mature in a separate tank, so I can add some height, but right now I'm perfectly satisfied.
You know, the tank is in my study where both myself and my wife sit and watch TV for longish periods during the day, but increasingly our eyes are on the tank. I didn't have a similar interaction with the tank when it was freshwater. Marine is the way to go for beauty and eye appeal.
AND IT WASN'T SO HARD, as is currently bandied about. It's just a watch on the water parameters to keep things nice and stable. I HOPE ........