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FAQs on Going from Freshwater to Brackish Systems 

Related Articles: Converting from Freshwater to Marine Set-Up,

Related FAQs: Freshwater to Marine 1Freshwater to Marine 2,

 

<FW to BR>; cycling       7/22/16
Hello all!
I wrote a few months back re: switching my freshwater tank to brackish due to an unexpected arrival, a green spotted puffer.
<Nice fish. Very intelligent.>
I intend to make the tank full saltwater, I even have a few Mollies in with him (4 or so in a 30 gallon).
<Mollies are hit-and-miss with GSPs; do keep the Puffer well fed with a good variety crunchy, filling foods (such as unshelled shrimp, used sparingly because of their Thiaminase content, and more frequently things like snails and whole lancefish). Hungry GSPs are more "bitey" than well-fed ones.>
Intend to move them to a 56 gallon.
<Good size.>
My question is this: at what point can I stop worrying about ruining my cycle.
<Good question!>
I did crash it the first time I added salt, then decided to go more slowly.
At what point (I'm at 1.008 sg) are the saltwater bacteria the dominant (or only) beneficial bacteria vs. freshwater bacteria?
<It's very difficult to pin down, but around 1.005 at 25 C I'd leave the tank to settle for a few months. Absolutely no reason to move GSPs above that salinity unless you want/need to. Once at SG 1.005, there'll be a balance of salt-adapted and freshwater-adapted bacteria, and you can make gradual changes upwards from that without major issues. Alternatively, as/when the GSPs are ready for full marine conditions, empty and break-down the tank, refill with full seawater, and rebuild using ample live rock, and live rock should "instantly" cycle a full marine aquarium without problems.
Make sense? Cheers, Neale.>

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