Help! From brackish to marine

[LilPuffy]

Hi, I thought is best to post in here since our problem is going from brackish to marine.
We were keeping and breeding angel fish for over 20 years, so we know how a fresh water tank works. Recently my son got two puffers a GSP and a F8 which are of course incompatible as marine environment, our aquarium was cycled and prepared for brackish water to receive the juvenile puffers. Now, our question as we also mentioned in "Meet and greet" section would be if we can acclimate this juveniles to be both full marine because we are going that direction, eventually we want the tank to be marine, the problem is we don't know in how long time to do this. We looked for articles and exact specifications but we couldn't find anything that tells us on how much to increase the salinity weekly or monthly and when (at which SG) to start adding the live rock and in which quantity.
We would greatly appreciate any help in how to slowly go from brackish water we have now for the juvenile puffers, the GSP is 1 1/4" and the F8 is 1" to full marine.
The filtration we have now is an external canister with mechanical filtration and biomax extra porous ceramic rings that works at about 180-200g/hour. We don't have any amonia or nitirte but the nitrates are at 10-15, we are doing partial water changes 1-2 times/week and rinse the ceramic rings in aquarium water, everything looks good so far but we don't have experience with brackish/salt water so we don't know what to expect....
The tank has fake decoration that we plan to remove and slowly replace with live rock also we are getting brackish water plants for now since I imagine we will have to keep the small puffers in brackish water for a good while before converting to marine?
We'd like to thank everyone in advance for their time and support

A&T

[RTR]

Sorry, but you have two incompatible fish co-housed temporarily. At and after sexual maturity, the GSP will be at least 2x the length of the F-8 or more and 4x or more it's mass. The GSP will harass or kill the F-8 most likely. As either of these fish can live 15-20+ years in captivity if properly maintained, you would be setting up a tank of disputes, harassment, and death. Don't shoot yourself in the foot. At full marine the GSP should be transitioned to a tank which is fish-only with live rock (FOWLR) plus Skimmer plus a 24/7 lighted marcoalgae refugium with only a fraction of the water changes required. For me, the F-8 should be kept in very light BW with specific gravity of 1.003-1.005 only. That tank will still employ freshwater nitrification bacteria and should be managed the same way as a FW tank with 50% weekly water changes. The FOWLR tank will require much smaller water partials due to its specialized biofiltration. If you do not want two tanks, I would suggest you return the F-8.

Unless I missed it, you have not specified your current specific gravity. If you must go through the transition range in either direction, you may need careful handling during the transition fro FW bacteria to SW nitrification bacteria, or from SW down to low BW conditions. That range is from ~specific gravity 1.007 to 1.012. There are articles in the library here which can help you with either transition.

HTH

[LilPuffy]

Thank you RTR, we are doing the reading to convert from BW to SW, we will end up returning the F8 after all. Hopefully everything will go well...

[Pufferpunk]

I think this is a good plan, LP!

[RTR]

I agree.