Switching from Freshwater to Brackish
Well, my latest sick Oscar has recovered (thank you Neale) and left this
afternoon for his new home.
So now I have an open 72 gallon tank that I would like to change
from freshwater to brackish for a dragon goby.
<Interesting choice. These big, quite friendly fish make good pets. They
are a little demanding in some ways, needing brackish water for example,
but in other regards extremely tough. Their biology in the wild is
fascinating. They live in tidal rivers where they are sometimes forced
to survive for hours in a wet burrow when the tide has gone out! So
unusually among marine fish they are able to breathe air. Many species
in their group lack eyes, and even the ones with eyes have such tiny
little eyes it's hard to imagine they see much. In the wild about half
their diet is reported to be algae and organic detritus, so needless to
say they're not fussy feeders, but their large size does mean they need
quite a bit of food.
Besides algae wafers and the like, they readily consume bloodworms,
brine shrimps, and other small invertebrates, but even the adults (which
can measure over 40 cm/16 inches) very rarely take live fish, even Guppy
fry, unless absolutely starving.>
I've done my research and spoke to the company I would be getting the
goby from and they say the fish (about 4 inches) is currently a
<Yes, often the case that they're shipped that way, but trust me, they
all come from estuaries and tidal mudflats. They are highly specialised
fish, rather like Mudskippers, that only 'make sense' in very specific
So my thinking is that I would get the fish, put it in my currently
freshwater 72 gallon tank, and slowly acclimate both the fish and the
tank to brackish water.
<That would work fine. You might want to change the decor of the tank
though, which you can do with the filter running. Depending on the
circumstances, you might want to remove any live plants (these are
unlikely to do well in brackish water) and replace gravel with smooth
silica sand (which these gobies like to burrow into). Rocks should be
smooth water worn cobbles to avoid scratching the goby, and the use of
hollow tube-shaped ornaments will provide useful hiding places. These
fish are rather shy initially, so shelter is important.>
But I want to be very careful doing this as I use RO/DI water with
Equilibrium and baking soda for a healthy pH/kH which has been working
<Unless your tap water has very high nitrates, there's really no
advantage to using RO water instead. Because you're adding minerals to
the tap water, and these fish demand high levels of dissolved minerals,
tap water rarely
presents any serious problems for brackish water fish. The exception is
high nitrate, which can cause algae problems. Otherwise things like
ammonia and copper in the water can be treated in the traditional way,
with a good water conditioner.>
I plan to use Instant Ocean to make the brackish water.
<A fine choice. But because brackish water fish are less demanding than
marines in terms of pH and mineral, even cheap generic sea salt brands
can be fine, and save you a few bucks over the years.>
I have sent e-mails to both Seachem and Instant Ocean telling them of my
plan and asking these same questions: 1) I normally do 20 - 25% water
changes weekly, Can I slowly acclimate the tank through my weekly water
changes or should I do it more quickly or more slowly than once a week?
<I would go much more slowly than this. Assuming the fish is in
freshwater now, I'd introduce the fish, and then immediately do a 25%
water change with water that has a salinity of SG 1.004-1.005. The
resulting salinity in
the tank should be around SG 1.001. That's fine for the first day or
I'd then do something similar, a 25% water change with SG 1.004-1.005
water, every other day. Crucially, this would result in the salinity
going up gently over the course of a week or so, allowing the filter
bacteria to adapt. Nobody really knows if marine aquarium bacteria,
brackish water bacteria, and freshwater bacteria are all the same things
or different species, so it's best to assume the latter, and allow the
tank to do a 'mini cycle' over the course of a few weeks. Once at SG
1.004-1.005, leave the tank alone for a couple of weeks at least. This
should be fine for the goby, and if he's feeding happily, there's no
need to raise the salinity further for a good while yet.>
2) will the Instant Ocean in the replacement water cause drastic changes
in pH/kH as it mixes with the water currently in the tank that contains
Equilibrium and baking soda or are there any other potential
between Equilibrium/baking soda/Instant Ocean that I should be aware of?
<There will be little difference in the pH before adding the salt and
afterwards, though it might go up a tiny bit. The hardness (both general
and carbonate) should go up a little too. But not enough to harm the
Similarly, while these changes will have an effect on your filter
bacteria, if you go slow, it won't be noticeable. Normally, there's no
need to add Equilibrium and baking soda to tanks with marine salt mix
marine salt mix essentially includes those two chemicals in its
3) in my research I came across a random post in a saltwater forum that
Instant Ocean is not sufficient to keep a healthy kH when used with
RO/DI water (this was a saltwater forum, not brackish) and that I would
use Seachem Alkaline buffer for that purpose. Would this be accurate for
a brackish tank?
<This is a debatable point, but worth thinking about. Normally, marine
salt mixes contain alkaline chemicals that buffer against pH changes, so
you shouldn't have to add anything extra, such as baking soda or a
alkaline buffer. But if you find the pH drops too quickly between water
changes, then you might need to do so. If we recall that pH drops are
caused by decaying organic matter in the tank, then if we have a
spacious tank that's well maintained, there's no reason to anticipate a
rapid drop in pH. Make sense? Bear in mind that these fish come from
highly variable habitats, and are MUCH less fussy about pH than their
marine cousins. So provided the pH doesn't go below, say, pH 7.5, you're
probably fine without adding anything beyond the marine salt mix.>
4) The information I've found said that the best SG for a dragon goby is
1.006, does that sound right to you?
<Anything between freshwater and full marine would be experienced in the
wild, so yes, 1.006 is fine. As noted earlier, I'd aim for 1.004-1.005
initially, simply to allow the bacteria in the filter to adapt. Once you
go above 1.005 you seem to get a mini-cycle kicking in, so I'd wait for
the goby to be settled in, and only change the salinity up if you feel
the need, and even then, in little steps through weekly water changes to
allow the filter to adapt. What you don't want is an ammonia spike. To
be fair, these fish actually handle high ammonia levels quite well,
being forced to live in wet burrows at times, but this isn't something
you want to deliberately cause for obvious reasons! Furthermore, your
final salinity might depend on your chosen tankmates. Many people keep
these gobies with
livebearers, whether Guppies or Mollies, since these 'dither fish' help
the goby feel more settled and secure, and add some colour and activity
to a tank that can sometimes seem a bit Spartan. Mollies are also good
I have buckets spread all over my bathroom and I'm going to start
testing as soon as I pick up some Instant Ocean tomorrow, but any
guidance you can provide would be greatly appreciated. I'd love to have
this fish, but I
have to be sure I can take care of it well before I jump in. Thank you!
<Hope this helps. These fish are genuinely not difficult to keep. But do
make sure they can't jump out: like most eel-shaped fish, this can be
risk if the tank has any large holes in the hood. Cheers, Neale.>
Re: Switching from Freshwater to Brackish
Thank you so much for all the information and guidance.
You've made getting this fish fun instead of stressful now that I have a
Attached is a picture of his/her tank.
It's a 72 gallon with a Fluval 405 canister filter on it.
<A good filter.>
Tank temperature is 78 degrees.
The substrate is pool filter sand and all the plants are plastic.
<Both good choices. Algae control may be a problem without live plants
though. Various approaches here, from the use of brackish water snails
(such as Batman and Spiny Nerite snails, Clithon corona, Clithon
sowerbyana, and Neripteron auriculata; also some US native species can
work too, e.g., Neritina reclivata) through to careful control of
lighting duration (4hrs on, 2hrs off, 4 hrs on) and nitrate control
(minimal food in, regular water changes out). Still, if you get the tank
right, with a good strong current in particular to keep down blue-green
algae, the only pest algae will be diatoms, and they're easily
controlled with Nerites.>
It's been up and cycled for a little over a year. It has a plastic egg
crate top that I cut specifically to fit this tank that did very well
keeping my Rope Fish in there when they had that tank.
It has a very snug fit to, so if the fish push on it, they won't be able
to move it. That mass of plastic plants in the center is actually
covering 4 - 2 inch pvc pipes, one on top of the other and fastened with
zip ties. One tube is 24 inches, the next up is 18, next is 12, and the
top tube is 6 inches. I know these fish get to be about 16 inches long,
but I don't know what to expect in terms of diameter, but I'm prepared
to make him/her a new "fish condo" out of 4 inch pvc if necessary.
<Understood. Juveniles should fit happily in the tubes you already have,
and under aquarium conditions they're unlikely to get quite so big as in
the wild. I think you're going to be fine for a couple years at least,
and should you need to upgrade, that shouldn't be hard to do. Any
ceramic ornament big enough for an adult Plec will be fine for an adult
Also, I have cut holes at 4 inch intervals along the tubes, about 1 inch
in diameter, on both sides to ensure water movement within the tube so
it doesn't stagnate. I can't find anything online that says these fish
like a strong current, so I do not have a powerhead in the tank.
<They do like strong currents, as do most gobies, but I'd be using a
strong current more to avoid blue-green algae than for the fish. Still
corners tend to be where blue-green algae starts off, and once in your
tank, it's a real pain to eliminate.>
I use RO/DI water for all the tanks because I'm on a well in a very
rural area and my tap water has 1 ppm of ammonia in it AND human remains
(probably wouldn't bother the fish, but it gives me the heebie-jeebies!)
<Understood, and yes, the fish couldn't care less. Ammonia will be
neutralised by a good quality water conditioner, and as for the human
remains, "parts-is-parts" so far as the biological filter goes. The
reason I often advocate against using RO or DI water is a cost issue:
people are more likely to do more frequent water changes if they can use
the cheap water from the tap. If they need to be spending money on RO
membranes, carbon filters, and all the rest of it, they're more likely
to minimise the use of new water for doing water changes. Ultimately
it's a balance. For sure, RO water is best, but 5 litres of tap water
trumps 1 litre of RO when it comes to water changes! Make sense?>
I actually have never tested the tap water for nitrite or nitrate.
<Neither are critical factors here, but if your nitrate is very high,
say, more than 20 mg/l, then algae problems are more of a risk, and you
should take precautions as mentioned above.>
So I ordered the fish and he should arrive Friday. I have to have him
delivered to the fish store where I get my supplies because UPS doesn't
come out to my house. When I pick up the fish, I'll pick up the Instant
Ocean and the store owner is going to loan me a refractometer until I
can afford to buy my own.
<Refractometers are nice an' all, but for brackish they're overkill. At
25 C/77 F, 1.005 water is about 8.9 gram marine salt mix per litre (1.18
oz per US gallon) and can be made up using kitchen scales using these
according to however much water your bucket holds. For example, a
5-gallon bucket would need 5 x 1.18 = 5.9 oz marine salt mix. Once
you've done that, and it's all dissolved nicely, a plain vanilla
hydrometer can be used to
check the specific gravity, and if the hydrometer is 'off' a point or
two, just make a note of that, perhaps by putting a permanent marker
line on the scale, and remember that's the level you want, not the
number on the scale.
Refractometers are fiddly and need calibrating, and don't, in
themselves, mean you're getting more accurate readings just because
they're more precise (accuracy and precision being completely different
Thank you for the suggestion about the Mollies for dither fish, but how
many should I get without pushing the stocking limits of this tank?
<Oh, for a tank this size you could safely start with 6-8 specimens and
let nature take its course. I'd get a single variety so that you can
share the offspring with local pet stores, Mollies being popular fish.
If you were feeling ambitious, you could get one of the two Sailfin
Molly species, as these occur alongside the Violet Goby in the wild, so
that'd been very authentic. Giant Sailfin Mollies in particular are
expensive and difficult to breed in freshwater, but in a brackish tank
will breed readily, adding value to your set-up. Alternatively, there
are things like Micropoecilia picta and Micropoecilia parae that are
very beautiful, difficult to keep in freshwater, and rare enough that
any offspring produced would be easily sold on. As their name suggests,
Micropoecilia are small, so you'd easily be able to keep a large group
of them in a tank this size. As we've discussed, Violet Gobies generally
ignore small fish, so you should be safe, but you might try out a few
Micropoecilia first before buying a whole
So as you read this, can you think of anything I've missed?
<See above! Cheers, Neale.>
Re: Switching from Freshwater to Brackish
Thank you again! Have a wonderful day!
<Off to the pub to meet a couple of friends, so that should be nice; my toddler
deciding to vomit all over the sofa, less of a highlight. Cheers, Neale.>
Re: Switching from Freshwater to Brackish 4/6/18
P.S. Per your suggestion, I just put a smaller powerhead in the tank. When I
moved the BGK and the Ropefish to my 125 gallon, I had to get them a bigger
powerhead. So I put their old one back in the 72. I don't remember the gph, but
it worked well for the BGK when it was in the 72 gallon.
<Should work fine. To combat blue-green algae, what you want is the water
*across the substrate* to be moving. So position the powerhead accordingly.>
Also, you mentioned the goby will need algae wafers for a balanced diet.
Will this fish also enjoy cucumber, zucchini, and peas like my Bristlenose
<Yes indeed. Violet Gobies are omnivorous, and very adaptable in captivity, but
all reports on wild specimens confirm that their stomachs are more than
half-filled with algae and organic detritus. In other words, very similar
to Plecs, and a similar diet should work nicely. Indeed, have odd little teeth
in their mouths that can be used to scrape rocks, and some aquarists have seen
them feed this way in their tanks. Cheers, Neale.>
Re: Switching from Freshwater to Brackish 4/6/18
Oh, I'm sorry about your sofa! But at least you have a little while before the
baby starts asking for the car keys!
Enjoy your day, and thank you again!
<Most welcome. Neale.>
<FW to BR>; cycling 7/22/16
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.
My question is this: at what point can I stop worrying about ruining my cycle.
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.>