Migrating FW tank to BW

[Vowyer]

Hi all. I've a 100l FW tank which housed 3 SAPs, 3 danios and some shrimp. I gave my SAPs to a friend with a bigger tank and now I want 2 F8 I found in a small cube in an LFS near home. I will change the substrate. So, questions:

1. Can I keep the existing bacteria colony in my filter?
2. How do I raise the salinity to around 1.005-6 without killing bacteria? O should I just start from scratch at the desired SG level with new bacteria and all?
3. How about decor? I had lots of plants with DIY CO2 system.
4. Is the salt brand important for BW? How much is it needed for my tank (i.e. how much should I buy?)

Thanks.

[nmonks]

If you're after figure-8s, why not keep the salinity at SG 1.003 @ 25 C, in which case your freshwater filter bacteria will adapt just fine. Do 20-25% water changes every weekend, replacing the water in the aquarium with SG 1.003 water. After a few weeks you should have salinity close enough to 1.003 without stressing either bacteria or salt-tolerant plants.

Since most of the plants that thrive in brackish water perform biogenic decalcification, CO2 fertilisation is largely redundant provided carbonate hardness is adequate.

Cheers, Neale

[Pufferpunk]

A decade-long experiment by our Mentor, RTR, Concluded that F8s do best in a SG of 1.005. You can add enough salt weekly to raise the SG .001-.002 without hurting your existing bacteria. I'd move the danios & shrimp the day the F8 moves in.

[nmonks]

Hi Jeni,

What RTR argues is that they do better in low-end brackish than freshwater. He hasn't compared SG 1.003 against SG 1.005 or SG 1.008 and declared any one of them better, so far as I know.

Cheers, Neale

A decade-long experiment by our Mentor, RTR, Concluded that F8s do best in a SG of 1.005.

[Pufferpunk]

Since none of us have seen this decade long study in writing, we really can't say what SGs he tested them in. At the moment, he's pretty much blind but when he's feeling better, I'll bug him again to publish his study.

[Vowyer]

At which SG the bacteria are different than the ones I have? If I go 1.005-6 gradually, will the FW bacteria survive?

Also, if it takes weeks to reach the desired SG, wouldn't be the same to start from scratch (considering I also have to empty the tank to change the substrate)?

[Brandon8521]

Your bacteria will acclimate to that sg without a problem as long as you dont raise the sg by more then .002 a week. No need to introduce new bacteria just worry about keeping the correct sg and it should be a smooth transition.

[nmonks]

Freshwater bacteria survive up to SG 1.003 @ 25 C, or 6 ppt, at which point they start to die off and get replaced by saltwater bacteria. See for example here:

Nitrifying Bacteria Facts

When raising the salinity from freshwater to brackish, you either keep it low enough the freshwater bacteria are happy, i.e., SG 1.003 @ 25 C, or else you carefully adjust conditions such that the die-off of the freshwater bacteria is compensated by the growth of saltwater bacteria. It's actually a bit more complicated that this, but for our purposes, having that idea in your head will give you a fair idea of what to do.

Cheers, Neale

[Pufferpunk]

Neale, Have you seen RTR's newest articles on bacteria in our library? Great reading!