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FAQs on Brackish Substrates

Related Articles: Brackish Components, FAQs on Brackish Salty Water, Brackish Water System Set-up Brackish Water Aquaria: 20 Questions; Yours Questions Answered by Neale Monks

Related FAQs: Brackish Filtration, Brackish Water Systems in General, Cycling a Brackish System,


Brackish Tank Questions; stkg., substrate, fdg.      4/15/16
Hi, I haven't had an aquarium in a while and I'm thinking about getting back into the hobby. In particular, I'd like to start a low-end (SG 1.002-1.003) brackish community tank in the 29 gallon aquarium sitting empty in my basement. I have some questions relating to stocking, substrate, and feeding.
<Fire away!>
First off, my tentative stocking plan is:
(1) Peacock spiny eel (Macrognathus siamensis) OR (1) Barred spiny eel (M. panacalus)
<Either should work here, though Macrognathus pancalus is arguably the more truly brackish of these species. Neither will want much salt though; 1.002 should be ample. Lower salinity will also ensure plants can grow well, especially Indian Fern, a definite plus here for stopping Spiny Eels from being jumpy.>
(1) Male and (2-3) female short-finned mollies
(2) Orange Chromides
<Generally fine, though as territorial as any other cichlid of this size.>
(1-3) Knight gobies
<Nice fish, and will ensure no baby mollies survive!>
Would this be overstocked?
<Nope. Busy, yes; overstocked, no. Just keep on top of filtration and water changes.>
I'm also concerned that in a 29, a pair of Chromides might become tyrants if they decided to breed.
<Always a risk.>
If you think that would be the case, I'll either reduce the Chromides to a singleton or remove them from the plan completely. (If you think this setup would be overstocked, they're also my first choice on what to eliminate.) I'm also wondering if even provided enough hiding spaces, the 29 might be too small for multiple knight gobies. How many do you think would be ideal for this setup?
<Two females and a male should be okay.>
On to substrate, I have a bag of CaribSea Sunset Gold sand laying around my house. Would that be soft enough for the spiny eel, or should I stick to buying some silica sand?
<I've not handled this brand of sand personally, but if it feels smooth rather than sharp, it's probably fine. That said, pool filter sand/smooth silica sand is so cheap, you might want to play it safe and go straight for that.>
Additionally, what depth of sand would be best to allow the spiny eel room to burrow but not to risk anaerobic decay? Does 2" sound about right?
<Sounds fine.>
As for feeding concerns, I want to make sure that the plant-based foods for the mollies and the meat-based foods for the other species wouldn't cause any health problems if the other party ate some of it. I also would like
some advice for feeding a balanced diet to the spiny eel and knight goby.
I know that spiny eels go crazy for earthworms, and I suspect that the knight goby would enjoy them, too.
<Yes! Very much so. Knight Gobies are very much predators.>
However, I'm a bit confused as to which of the big three in aquatic feeder worms (bloodworms, blackworms, and Tubifex worms) is most nutritious and least likely to carry diseases.
<Not much in it, to be honest. Tubifex have a very bad reputation, probably justified. But bloodworms and blackworms aren't exactly cultured in crystal clear pools of French mineral water! On the other hand, if gamma
irradiated, they shouldn't carry any pathogens, and if used sparingly, the risk from introducing heavy metals, for example, shouldn't be too serious.
That said, marine aquarium foods like krill and fortified brine shrimp are certainly safer and usually accepted readily.>
I've seen claims in favor of or against all three of them, even here on Wet Web Media. I'd sort of like to start a culture of one of these in one of the smaller empty tanks as an easy source of live food, but I don't know which would be best for the fish.
<If you're growing them yourself, they're probably all reasonably safe.>
I intend to buy wet-frozen krill as another food for the goby.
Do you think that the eel would also eat those?
<Yes; spiny eels are hesitant feeders, and nocturnal to boot, but they aren't over-fussy. My specimens have happily taken chunks of prawn, for
I also know that any and all molly fry will probably end up knight goby
<Oh yes!>
What other foods would be good for one or both of them?
<See above.>
Some of the things I commonly see suggested, such as lobster eggs, aren't available in my area as far as I know,
<Do try stores aimed at marine aquarists.>
and others, like tilapia, I don't think my parents would approve of buying seafood sold for human use to feed to pets.
<So far as seafood goes, one approach is to buy white fish or squid for yourself, and wrap the scraps in some aluminium foil and place it in the freezer. Your fish aren't fussy, and for a few weeks at least such scraps will contain sufficient useful nutrition.>
If I do get the Chromides, I plan on using one or two brands of cichlid pellet or flake food for a staple, in addition to the smaller varieties of worms.
Finally, for the mollies I'll provide some sort of spirula-based flake food, and maybe algae tablets, but I'd also like to give them fresh veggies. When I see stuff like this mentioned, I always hear that you should blanch the vegetables and put them in the tank when they've cooled off, but I never see any recommendation for how long to cook the veggies.
Is there some sort of good rule of thumb for that?
<None. The blanching thing is about softening, not cooking. Zapping lettuce in the microwave for a few seconds usually does the trick. But lettuce is nutrient poor and shouldn't be anything more than a "salad bar" that goes
along with the main course, i.e., the good quality flake. Some foods, like cucumber, can be left in the tank to soften naturally, and the fish will peck away at over time. Since these foods contain near-zero protein, their impact on water quality is minimal, even if they end up as horrible mush.>
Thanks for the help.
<Welcome. Sounds a nice tank and well planned! Cheers, Neale.>

Substrate sand....small brackish  - 12/02/2012
One more quick question before I disappear again for a while.....
I plan to put the two baby 1/4" balloon mollies into a true brackish environment.
I will acclimate them gradually of course.
<No need. Assuming specific gravity is going from freshwater (SG 1.000) to low salinity brackish (SG 1.002-1.003, ample for Mollies) then you can literally dump them into the tank!>
(They were kept with aquarium salt before I knew better. I plan to use the marine blend salt this time, and I'll use the meter to check the salinity.) I decided to do the brackish in a smaller tank that I have, and then I'll restock the 29 gallon with another type of fish to start out.... I'll probably choose the simplest kind of fish for the 29 gallon this time around.
I'm interested in using sand in the brackish tank. I read your article on WetWebMedia on substrate, and I also read this other article that gets a little more in detail on the handling of sand substrate on a cichlid site:
I like the idea of sand for the look, and it's nice for the small shrimp that will be the 2 baby mollies' only tank mates in the smaller tank. Black sand seems cool.
<Can be; shop carefully though. If you plan on adding any digging fish (say, gobies) then some "sharp" black sands, like Tahitian Moon Sand, aren't ideal. On the other hand, midwater fish and shrimps will be fine with whatever black sand you choose.>
Fish tend to like a dark substrate and it's attractive. Though, I also like the idea of coral sand that you mentioned in your article which is excellent for buffering.  White also sparkles nicely.
<But yes, with freshwater fish, the colours fade a bit. Not an issue with Mollies since the colours are hard-wired into them, but it's noticeable how (some) cichlids for example "fade" in tanks with a white substrate. Not all by any means, but some species.>
Either color works for me.  (I just don't have undergravel filter like you suggest though, I use a regular submersed one.  So it could work out differently I suppose….) (Would coral sand be too bright for mollies and shrimp, would it be likely to stress out my fish?)
<Will be fine. For one thing, the sand de-colours with age, becoming more off-white, even greenish.>
Also, the that stuff this guy in the cichlid article mentions about gasses building up worries me a little, I don't know.....  !  You have to disturb it periodically.  As I'm a beginner, I don't want to mess up the tank's chemistry accidentally!  Sounds like he is not afraid of it though.
<Quite so. The "deadly gas in the sand" idea is mostly a myth. It's theoretically possible if you have, say, 8 cm/3 inches of sand. But if all you're doing is adding enough sand to cover the glass, then gas isn't likely to accumulate to any great degree. Even where deep sand beds *are* used, this deadly gas problem just doesn't seem to happen, and in fact, there are positive benefits to deep sand beds!>
SO, my questions for you regarding a proper substrate are:
1) would mixing a little coral sand with fine gravel like you suggest avoid a buildup of gasses that using a straight coral sand for substrate might incur?  Maybe this is the simplest approach that would give me some sandy look, but be lower maintenance than a thick sand bed that tends to compact in the absence of burrowing species?
<Personally, I'd go with 2.5 cm/1 inch of sand, maybe with some coral sand stirred in if you want. Easy to clean and risk-free.>
Or--2) would using a bare minimum of coral sand, or even just the black sand, and just using it in a thin layer (perhaps 1/2 inch) and then stirring it a bit weekly, help to avoid a gas buildup under the sand?  My main concern with sand substrate is if I accidentally allowed too much gas to accumulate and then the fish become ill or die.
<Just doesn't seem to happen. The deadly gas is hydrogen sulphide, but in practise, this gas becomes oxidised so readily when it emerges from the sand that it's hard to get enough in the water to stress fish. Look at ponds; they have thick, anoxic mud, yet the fish are fine.>
It sounds like the trick to vacuuming sand is to stay a half inch above....maybe I could disturb the sand all around, and then wait till it settled and do the vacuuming about an hour later to catch excess debris I stirred up?  Or is there some important reason that the article I read says you should wait 8 weeks in between disturbing the sand substrate?!?!
<I have no idea. I don't bother. I put the sand in and leave it there. But I do tend to use snails and/or plants to keep the substrate biologically "active".>
Those are just guesses of mine, but you know the actual science...I feel that possibly using sand sparingly with regular agitation might be a lower maintenance and safe way for a beginner to work with sand, but I don't truly know. With gardening I've always strived to take the easiest approach.  Perhaps that really IS just plain old gravel in fish keeping.
<Can be. But sand has definite plusses.>
But if there's a way for a beginner to keep sand without a lot of trouble, I'd like to try it in my smaller brackish setup.
<Hmm… do read more on substrates, here:
Cheers, Neale.>
Re: Substrate sand....small brackish  - 12/02/2012

Thanks, this is very helpful.
Have a nice week and happy holidays too.
<You too, Neale.>

BW Substrate Questions  5/5/07 Thanks for the help again. <No problem!> I have gotten a root from PetSmart today and it looks great. I am going to go with the crushed coral to help  buffer the PH and also I like the bright colors of my GSP. That is when I realized I had a couple more questions. The first is: how to I calculate how much of the crushed coral I will need in lbs? My aquarium is 30long x 12 deep x 18 tall. <About 1lb/gallon.> The second is: I bought a few plants online and noticed they have a ceramic base to them, are they ok to use in the tank. <Shouldn't be a problem.> My last question is: When I change to the crushed coral should I leave some of the old gravel underneath? <I wouldn't.  Change it all out.> Once again thank you all, I get tons of info for myself and for my daughter's freshwater and I always recommend you all to anyone I run into that needs some help. Thanks again and keep up the great work. <Glad we're so much help to you & your young'n!  ~PP>

Old Florida Crushed Coral Safe For Brackish Tank?  2/14/07 Hello, <Hi Tom, Pufferpunk here> I love your site! Could you tell me if it is alright to use Florida crushed coral (the bags are about 20 years old, from a saltwater system I was going to do that long ago, and didn't)? It is white, not like the yellowish substrate they sell now. <I don't see why not, as long as it hasn't been used before.  Make sure you rinse it well, to avoid too much clouding of the tank.> I'm planning to have 1 mudskipper and 2 or 3 small mangrove seedlings I have (I have a bunch of seedlings I grow in pots around the house in fresh water) in a 20 gallon aquarium. <Make sure that tank is a 20 long, not a 20 high.  A 30g would be even better.  Try for one of the smaller species of mudskippers.  I always worry about a skipper climbing up the mangroves to the outside.> Would you suggest just rocks to build up a beach effect for the fish or what? <Rocks are fine.> I have  a few flat rocks that look like red sandstone (or at least they are dark red and heavy) and one that looks like something out of a King Kong movie (the rock formation he dreams of. :-) Do you think these are safe for a brackish system? I tried splashing plain vinegar on them and didn't see any bubbles (remembered from Earth Science days in High School a million years ago). <Sounds OK to me.> What would be some alternatives? Thanks for your time and again I love your site! <If you wanted to set it up for biological filtration, find something to hold gravel back behind the rockwork & bury a powerhead with a prefilter attached under crushed coral/gravel, making a waterfall from the output.  This looks great but would need to be torn down & cleaned every 4-6 months.  The larger the tank, the less poop will clog this system.  This is the powerhead I was thinking of: http://www.bigalsonline.com/BigAlsUS/ctl3684/cp18554/si1382178/cl0/marinelandpowerhead660r  ~PP> Tom

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