Contrasting FW and SW methods

[zanzimog]

Although there are exceptions, it seems like most people want to master a FW tank or two before making the move to SW. When one makes the transition from FW to SW, what are the differences, or the similarities? In other words, what new tricks does a FW keeper need to learn?

Naturally, there are many ways to do both FW and SW. In FW, one could have anything from an UG filter and plastic plants to a heavily planted biotope with metal halides, CO2 injection and multiple monitors and contollers. Similarly, SW tanks can range from a FO (fish-only) tank with a wet/dry filter, to a full-blown reef, with lots of things in between. Are there any generalizations that can be made?

To start with, all tanks have a nitrogen cycle. The species of bacteria are different, but the process of turning toxic ammonia (NH3) to more benign nitrate (NO3) is roughly the same. What happens to that NO3 can be very different, however.

One difference is that for many FW tanks the only exit for NO3 is regular partial water changes. In contrast, most SW tanks contain live rock, which provides hypoxic or anoxic regions where NO3 can be reduced to N2 or NO, and bubble off as gas. Another exit can be via plants. FW planted aquaria are so efficient at removing nitrogen that NO3 often has to be added to keep up with plant growth. Not wanting to be left behind, many SW aquarists are now creating tanks with emphasis on marine plants and macroalogae, rather than corals. Related to this is the common use of refugia, tanks connected to display aquaria that contain macroalgae, rubble, sand, etc, to make use of the plants to export nutrients and provide a safe place for small, tasty organisms to propagate.

That's a start, but there's lots more to be said. Please chime in with comments and questions; we have the whole month!

[wesleydnunder]

I've been researching and gathering equip. for the last couple of years in prep. for a 125g reef with some help from a local reefer's club. One thing that intrigues me is the total absence of canister filters in reef set-ups. The unanimous opinion seems to be that canisters are nitrate factories, and so, undesirable. Also, Reefers seem to do more topping off than changing water. One guy claims to have not done a water change on his reef in ten years, yet his tank is gorgeous. I'm told by some of them that having a basic understanding of FW, I have less to learn but more to un-learn than someone who has never kept any aquaria.

Mark

[OrionGirl]

I think one of the similarities is that patience is pretty critical for both. Another generality that applies to all the tanks is that the more planning and research that's done in advance, the smoother and easier the whole process becomes.

One of the biggest differences I've found is that there are a wider variety of stocking choices for a small to mid-sized FW tank than for SW. There are lots of fish that will work well in say a 30 gallon FW setup, but far fewer SW fish that will really thrive in a 30.

And of course, there are way more invertebrate options for SW than for FW, although that's starting to change as more and more FW species of shrimps become available.

[zanzimog]

One thing that intrigues me is the total absence of canister filters in reef set-ups. The unanimous opinion seems to be that canisters are nitrate factories, and so, undesirable.

I wouldn't use one, but some people do. Interestingly, it seems like a lot of people posting "I have a lot of nitrate" threads have canister filters. Intriguing correlation.

But that does bring up the whole issue of filtration. I don't use any mechanical filtration, on the belief (note that I don't call it fact) that mechanical filtration traps debris and allows it to rot and and turn into nutrients for algae. There are a lot of animals in a healthy marine tank that will take care of debris in the water column and on/in the substrate, so I tend not to worry much about it. Plus, mechanical filtration extracts plankton from the water, and I would prefer that the corals and filter feeders get it.

So what's left? Well, there's chemical filtration. Many marine aquarists use activated carbon. One positive effect is that it removes molecules that color the water, helping light to penetrate and making the tank look better. Another benefit is that it can interfere with chemical warfare between corals. Many corals secrete chemicals into the water to inhibit other corals from growing in order to compete for space on a reef. This can potentially cause trouble in a closed system, and carbon will help to remove the compounds. In order for it to do its job well, it needs to be replaced regularly, as in every week. There are potential negative effects, such as removal of desirable compounds, but that seems to be more in the realm of theory than hard data (but I will be happy if you can find something to contradict me).

The other major form of chemical filtration is protein skimming. The principle is simple: many organic molecules act as surfactants, collecting at the interface between air and water. Generating a froth of bubbles, and allowing it to progress up a column will draw organic sludge with it. The sludge is then delivered to a collector at the top of the column. Skimmers will work on FW tanks, but are much less effective for a variety of reasons. On the other hand, skimming is a very effective way of removing organics from a SW tank, and most tanks benefit from being skimmed. In addition to removing impurities, a protein skimmer also aerates the water intensely, yet the aeration occurs in an enclosed column, preventing the splash from the bubbles from causing salt creep.

Originally Posted by wesleydnunder

, Reefers seem to do more topping off than changing water. One guy claims to have not done a water change on his reef in ten years, yet his tank is gorgeous. I'm told by some of them that having a basic understanding of FW, I have less to learn but more to un-learn than someone who has never kept any aquaria.

You definitely have to pay more attention to topping off, but the whole water change thing is controversial. Over time, trace elements get depleted, and I prefer partial water changes every week or two to gambling with trace element additives.

[Zoolander]

Interesting thread, I will enjoy following this one.

[RTR]

Bacterial biofilters are nitrate factories - that is their kob, what they are intended to do. You can't fault a tool for doing its job. It is a needed job in some setups either FW or SW, depending on the setup. All creature produce waste. In a semi-closed dystem, that waste will poison the vritters which produced it (if it were not waste and by definition toxic, They would retain it as an intermediary metabolite - they cannot with high energy cost, so they dump the material). If there are other processes in the setup to handle (either oxidize or reduce) nitrogenous waste, then bacterial biofilters may not be needed or even desirable in either SW or FW. Live rock and skimmers in SW. planted tanks in FW, or lighted refugia in either condition can do the same job without leaving a follow-up job of removing the resuting ozidized nitrogen material from the water..

Back when I did SW, i used sumps/refugia on most setups, over-the-back types, with sponge prefilters. I learned early that daily rinsing of those prefilter sponges was the best/cheapest/easiest technique I did for water quality. The issue already mentioned of sponges (or other particle-traping media) being waste digesters is real. If you have no other tcehique for getting particulates out or used, keep any collection devices you have as clean as is possible or practical. Skipping a day is not going to bring the house dowm, but if you are there looking at the tank, how much time does a quick rinse need? Cheap and easy I like. Cleaning skimmer cups should be so simple...

Aside - refugia/refugium do not have to be lighted. The concept only involves a separate vessel for some protected process. Regugia with 24/7 lighed macroalgae are justifiably popular now, but they are just one application of a class. I use refugia routinely, for fry, as plant/algae filters, for equipment undesirable in the display, multiple refugia use multiple techniques, lighting for plants or algae being only one of those techniques.

[zanzimog]

Although it may sound obvious, water chemistry is indeed very different between FW and SW tanks.

First, there's the starting material. When wearing my FW aquarist hat, I largely rely on what comes out of the tap to dictate the chemistry of my tank water. I dechlorinate/dechloraminate, add some ferts for the plants, and buffer the water for the Tanganyikans, but the ionic composition of my tanks is largely up to Washington Suburban Sanitary Commission. There are certainly cases in which FW aquarists take greater pains, but I would venture that most approach water chemistry in a similar way.

On the other hand, the chemistry of SW tanks is a rough approximation of that of the ocean. This can either be accomplished through the use of natural SW or synthetic mixes. There are companies that sell natural SW, which is generally only economically feasible for small tanks. Alternatively, some are lucky enough to live near research instituions, such as Scripps Institution of Oceanography, where filtered seawater is available free of charge from a public tap.

Most of us, however, use synthetic mixes. There are many on the market, and most are more than adequate to provide a healthy environment for fish and corals. Occasional wild claims are made about toxic effects of one mix or another, but these are rarely substantiated by later tests. Essentially, a good salt mix provides all of the major, minor and trace elements needed by your livestock, so there is no need for buffers, additives or anything else. That is not to say things will not get depleted over time, just that the mixes are essentially complete at the beginning.

Although the salt mix does not depend on the source water for any of its components, the water one uses can have a significant impact on the health and success of the tank. Tap water generally contains chlorine or chloramine, which obviously need to be removed. Further, tap water can also be a significant source of toxic metals, as well as nitrate and phosphate, which can feed nasty algae blooms. There are some places in which tap water is perfectly acceptable after dechlorination, so what you need to do with your water depends a lot on where you are.

Because my water source is not that good, I water run through a reverse osmosis (RO) unit, followed by a deionization (DI) cartridge. The combination is referred to as RO/DI. An average RO system has several stages. The first stage filters out particulate material. The second stage is usually a block of activated carbon, to get rid of chlorine or chloramine, which will damage the RO membrane. The RO membrane itself is a sheet of synthetic material full of holes so tiny that they exclude contaminants at the molecular level. This removes the vast majority of dissolved material in the source water, but some compounds, such as phosphate, can pass through to some extent. To do a final polishing, many use a DI cartridge, which contains a resin that exchanges one charged molecule for another of similar charge. In other words, a charged molecule you would rather not have in the tank (like phosphate) sticks to the resin and displaces another charged molecule that is less of a problem (like hydroxide ion). The end product, then, is water that has had the vast majority of debris and dissolved material removed.

So, then, all one needs to do is add the salt mix to the water in the recommended amount, right? Yes and no. Regardless of the accuracy of your measurements, you will need to check the specific gravity (SG) and/or salinity with a hydrometer or refractometer. Hydrometers use the fact that salt makes water more dense, i.e., increases its SG. By looking at how high an object of known density floats (either a swinging arm in a box, or a bouyant glass bulb), you can tell the SG of the water. Normal seawater is about 2.5% more dense than pure water at room temperature, so its SG is 1.025.

Because SG is highly dependent on temperature, and because hydrometers tend to be cheap and poorly calibrated, increasing numbers of aquarists are using refractometers. Instead of using density, refractomers make use of the way salt changes how water refracts light, and give a direct readout of salinity (measured in parts per thousand, ppt). Most refractometers are temperature compensated as well. Refractometers are significantly more expensive than hydrometers, but are worth it for the increased accuracy and peace of mind.

The water is mixed, the salinity is right, now what? Lots. Water changes, calcium, carbonate, alkalinity/buffering and more! Stay tuned.