Saltwater tank idea - Tropical Fish Keeping - Aquarium fish care and resources
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post #1 of 9 Old 09-28-2008, 01:07 PM Thread Starter
iamntbatman's Avatar
Saltwater tank idea

I have a 20 gallon long tank laying around that I've been tossing around ideas for. The big two are freshwater: a river biotope or possibly shelldwellers. I've been reading the saltwater section a lot more lately and I feel that I've learned a lot.

I understand that it's desirable to have an aquarium with a more complete nitrogen cycle in a marine aquarium, i.e. one that contains a deep sand bed and enough live rock to house anaerobic bacteria that convert nitrate to nitrogen gas. I understand that a system with little to no nitrates is essential to healthy coral growth.

What I'm not clear on, however, is the relationship between low nitrates and healthy marine fish. Why do marine fish, in general, have a lower tolerance for nitrate than freshwater fish? What species, if any, can tolerate higher nitrate leves? I'm not talking out-of-control, through the roof nitrates, but levels typical of a well-maintained freshwater system, in the 10-15 ppm range.

The reason I ask is that, if possible, I would like to at least have the possibility of using the 20g long as a marine tank with fish only. I don't want to do a full-blown reef tank or even FOWLR because I'm not sure exactly how long I'll be living where I do, as I might be moving sometime in the relatively near future for graduate school and/or work. I don't want to invest a huge amount of money into a reef tank and not be able to take it with me.

The other thing I've considered is cost-related: with marine mix being as expensive as it is, how long would a fish-only (no live rock, standard freshwater-type filtration) system be able to run before the cost of doing (larger and more frequent) water changes eventually exceeded what the initial cost would be of using a deep sand bed, live rock and protein skimmer?

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post #2 of 9 Old 09-28-2008, 01:16 PM
Well, those are some interesting questions you asked.

I want to say this (and I know some people will feel completely against this)...SW is definatley not as hard and stressful as people think. DSB's are a plus, and it does do what you say, but is not needed at all. In my next tank, I would go bare-bottom, but I am only getting a very thin layer of sand for looks.

As for the tolerance level of marine fish, I have no idea. I have never come across anything that says that. My guess would be it is because of all the organisms in the water, if that makes an sense..

And, I have seen many reef systems (yes, reef), that has 5, 10, sometimes evn close to 20ppm of Nitrates and still do very successful. Having 5-10ppm of nitrates is perfectly acceptable IMO. This would mean plenty of fish would do fine with this level.

And for the FO system, I will need to do some research for you. I know plenty of things about reef systems, but I am limited on FW equipment on a SW enviroment.
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post #3 of 9 Old 10-01-2008, 10:32 AM Thread Starter
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I'm not afraid of the "difficulty," just of the financial investment in a tank that's likely going to get torn down in a year.

Thanks for the other info; that's reassuring.

Anyone else know much about doing this kind of thing?

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post #4 of 9 Old 10-03-2008, 10:39 PM
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hey batman, I'll toss in my two cents here, and I'll try to avoid saying anything I'm not pretty sure is correct.

I agree with Cody, unless you plan on getting fish that you have specifically read do not tolerate high nitrate levels, you can successfully keep a FO tank with nitrates in the 10-20ppm range.

Also about the sandbed I agree with Cody, if you don't want to go DSB, then go with an inch or less on the bottom... the medium-depths (~3") of sand are the bad spots to be in... too shallow to allow anaerobic bacteria to grow, but deep enough to trap a lot of waste, etc. and cause higher nitrate levels.

Salt mix isn't THAT expensive, you can get a 40lb-50lb bag of Instant Ocean that will last you a long time with a 20 gal. What CAN be more expensive, or if not more expensive simply more of a pain, is keeping a stock of RO water handy. If you don't want to buy a $200+ RO unit for your home, you have to buy it from your LFS. While cheap, its a bit of a hassle toting 5 gal buckets back and forth from the store. But for SW, RO is the way to go, if you want to avoid a bunch of really ugly algae growth.

I guess in summary, if you just wanted to set up a simple 20 gal FO SW tank for a year or so, I say go for it. It'll be a good learning experience for someone who loves fishkeeping! The fish are absolutely beautiful. It won't be THAT much more expensive (the fish will be though!), and if you're willing to deal with keeping a stock of RO water, properly premixing your saltwater before water changes, etc, then it'll be very much worth it for you :).

Can you give more details on exactly what kind of filtration you would use for it? You said FW-style filtration, so are you planning something like the classic aquaclear or similar filter with a sponge, carbon, and maybe ceramic stuff for bacteria growth? Let us know what you decide!

"To an optimist, the glass is half-full;
to a pessimist, the glass is half-empty;
to an engineer, the glass is twice as big as it needs to be"
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post #5 of 9 Old 10-04-2008, 09:56 AM
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Originally Posted by conger
Also about the sandbed I agree with Cody, if you don't want to go DSB, then go with an inch or less on the bottom... the medium-depths (~3") of sand are the bad spots to be in... too shallow to allow anaerobic bacteria to grow, but deep enough to trap a lot of waste, etc. and cause higher nitrate levels.
Agreed. Great point. Moving on...

The idea of keeping Nitrates low in a marine aquarium really isn't much different than Freshwater. The difference is the sensitivity of the fish to changes in their environment. You could certainly use a biological filter on a small saltwater aquarium and achieve acceptable Nitrates with frequent water changes. In a small aquarium, this might even be cost effective, especially if the aquarium is lightly stocked.

It is very difficult to point to fish which tolerate high Nitrates and fish that do not. You really can't make a statement such as "Coral Beauty Angels will thrive with Nitrate readings not to exceed 20ppm." It just isn't that simple. The entire aquatic environment that is created will determine the ability to keep the fish.

Ok, follow me on this point. This is how I explain this situation in person. Pretend you have a bag full of 1000 white golf balls. Every time you make a decision that increases the stress level within the aquarium, you have to replace a white ball with a red ball. Now, every morning you have to reach in the bag and pull out a ball. If you pull a white ball, the fish are healthy. If you pull a red ball, the fish are dead.

So, you want to use a biological filter. The filter itself is not a stress factor. However, your pH will be less stable. Red ball. Your alkalinity levels will be harder to maintain, resulting in many bad things beyond the scope of this question. Red ball. Nitrates will accumulate faster. Red ball. More frequent water changes will be necessary, which is a stress on the fish. Red ball. Your aquarium is small to begin with, causing territorial stress. Red ball. Salinity changes are increased due to evaporation on a small tank. Red ball. You are new to the marine hobby and won't recognize fish behaviors effectively. Red ball. You don't have a quarantine tank. Red ball. Say you decide to keep 2 fish, rather than 1. Red ball. Say you try to keep a fish that really doesn't belong in a 20 gallon tank, like a Flame Angel. 3 Red balls. Say you decide to only feed a staple food, rather than a good mixed variety. 3 Red balls. Say you skip Live Rock completely, not recognizing the value it adds to the fish diet and overall comfort level. 20 Red balls.

You get the point.

Your easy option would be better to use Live Rock as the sole source of filtration, placed on a thin layer of sand, with a single power head for water movement. Add one or two very passive small fish, a few snails and crabs, and you have a nice display. You could even use a small internal protein skimmer driven by an air pump if you like. Personally, I would never skip on the skimmer. Never.

Bottom line, why use any type of filter that pumps Nitrates into the tank. It just isn't necessary. And you will have enough challenges on your hand in a small aquarium environment.
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post #6 of 9 Old 10-04-2008, 11:40 AM Thread Starter
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Thanks guys, great points.

Pasfur, why do you suggest going with the thin sand layer and live rock instead of a DSB?

Also, I really like the way live rock looks when it has good coralline growth, but not ugly, dead, white rock. Since I'm not going to be doing any sort of corals just yet, I'll probably have some pretty cheapo lighting. How much will this impact growth of stuff on the rocks?

Also, what are some interesting fish ideas for a tank like this? Another reason I wanted to see what kind of responses I'd get are because I like a lot of fish that are generally considered non-reef safe, and I figured as long as I'm excluding the possibility of a reef anyway, why not consider these fish?

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post #7 of 9 Old 10-04-2008, 03:44 PM
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well jim, im glad you dropped the pepper and your picking up the salt.

welcome to a whole new world. you may just never turn back from here.

my guess why salt water fish do not tolerate high nitrate levels would be because pretty much all of them are caught from their wild habitat ( what a shame for alot of the over harvested species ) anyways if you look at this such habitat- it is HUGE, theres more water on earth then land so the nitrate is so diluted the levels are non-existant.
^ that however is my educated guess
and i would say shrimp are of the more sensitive critters

i think a pair of tank raised clowns would be perfect for a 20gal.
reason for them being tank raised is because they for 1 arnt being ripped from their natural home, 2 they seem to be more hardier and 3 clowns are amusing to watch, but i know it seems like everyone goes with a clown fish...but 20gal you'll have some restrictions as the oxygen content isnt the same with freshwater so stocking wise is less.

im unsure of the growth of coraline with stock lighting as ive never used it on my system, i do however know they need good alk,calcium and mag. levels for sufficient growth.
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post #8 of 9 Old 10-04-2008, 04:48 PM Thread Starter
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Don't think I've given up on freshwater - this is only an idea, and is still competing with my other two (freshwater) ideas for the tank. Even if it does turn out to be a salt tank, freshwater will always be my main focus.

Nitrate levels in natural freshwater environments of any considerable size (i.e. larger than a puddle) are usually pegged at zero, due to the presence of so many plants and so much algae.

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post #9 of 9 Old 10-04-2008, 06:17 PM
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Originally Posted by iamntbatman
Pasfur, why do you suggest going with the thin sand layer and live rock instead of a DSB?
I don't. I'm just along for the ride on this thread and given that you only have a 20 gallon long aquarium, which is very shallow, I don't think you will want to give up 4'' of height. Also, your interest is in the short term, not the long term. Given that you are just getting your feet wet and having some fun with a saltwater setup, you could save the expense of additional sand.

Now, here is a very important point on fish that is often overlooked. This is one of the big reasons the beginner has a hard time in the marine hobby. Almost every Nitrate tolerant fish, meaning most of the hardy marine species, grow very large. These include Triggerfish, Puffers, Groupers, Eels, Lionfish, etc. If you want an "easy" marine tank, then you need a BIG tank. Unfortunately, most beginners want to try something small first, which means you are dealing with more sensitive species. The only small fish that can be considered as easy to keep as the fish I name above are Damsels and Clownfish. The problem here is the extreme territorial behavior of Damsels, which pretty much leaves you keeping a pair of Clownfish, if you want something "easy" to keep.

So, by choosing a small aquarium and probably wanting something other than Clownfish, you should definitely go with some Live Rock. When you think of easy to keep saltwater fish, we should really add "easy with live rock" and "easy without live rock". Many of the smaller species of fish become relatively easy to keep in a system that has Live Rock. These same fish would be very difficult to keep in a system without Live Rock. A great example of this are the Centropyge angelfish species.

I also am not a big fan of the appearance of Live Rock. My reef setup has artificial coral decorations mixed in with the Live Rock. I personally like the display it creates, and after all, I am the one who I am trying to please with my tank!-)

As for coraline algae, you should get coraline to grow on the Live Rock if you keep your alkalinity and calcium levels in check, which is vital for every marine system, fish only or reef.
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