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FAQs on Going from Freshwater to Brackish Systems & Vice Versa

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

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


Brackish to Freshwater; lost Violet Goby; Fire Eel sys.       8/8/18
Hello Crew.
I lost my Violet Goby today. He was in the tank when I did his water change last night, but when I went to feed him this morning, I couldn't find him. When I did find him, he had gotten out of the tank and wiggled into my closet. He was very dried out, but I tried floating him in the tank in a net all day - but he was gone.
<How cow! That's bad news indeed. Sounded a great fish.>
I've decided I'm not going to get another one, at least for now, and to convert that tank back to freshwater. I sent you a post a few days ago about compatibility between my BGK and a Fire Eel I will be getting from my friend this Saturday, and instead of putting it in with the BGK, I'm going to put the Fire Eel in the goby's old tank. My question is, how sensitive are Fire Eels to salt?
<Not especially, but they don't want brackish. On the other hand, a trivial amount is actually quite therapeutic, and a safer treatment for Whitespot and Velvet than the alternatives. Certainly, the addition of 1-2 gram salt per litre of water has been standard operating practise in Europe when keeping Spiny Eels of all kinds, including these.>
This tank is low end brackish, SG 1.005. Do I have to completely rinse out the tank, sand, filters, everything and start over, or can I replace the water, or a portion of the water, to drop the salinity as low as it can go without destroying the biological filter that currently exists in the tank.
<A succession of water changes will be fine, which I'd do across a couple of days to allow the filter to adapt. Keep adding a little flake or something to keep the filter bacteria ticking over. Once the salinity is
1.001 or less, you can add a Spiny Eel without problems. Cheers, Neale.>
Re: Brackish to Freshwater      8/8/18

Thank you!
<Most welcome! Neale.>
Re: Brackish to Freshwater      8/8/18

Thank you!
<PS. If a Violet Goby jumped out of your tank, a Spiny Eel will definitely do so. They are notorious escape artists. Double check every hole is sealed off with plastic mesh, filter wool, or something else that lets air through but nothing else! Cheers, Neale.>

Switching from Freshwater to Brackish    4/4/18
Hello Crew!
<Hello Renee,>
Well, my latest sick Oscar has recovered (thank you Neale) and left this afternoon for his new home.
<Well done!>
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 freshwater fish.
<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 situations.>
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 very well.
<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 two.
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 interactions
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 fish.
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 added, because
marine salt mix essentially includes those two chemicals in its formula.>
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 need to
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 commercial
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 for algae
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      4/5/18
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 plan!
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 Violet Goby.>
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 values
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 things).>
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      4/6/18
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 Plecos do?
<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
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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