Saltwater Aquarium FAQs

I get a number of emails every week from readers of I’ve always made it a point to answer each email personally, or at the very least, redirect the reader to another site if a more lengthy answer was required.

This series of FAQs are based on some of the questions that found their way into my email inbox.

Keep sending those questions in to!

Saltwater Aquarium FAQs #1:

1. How deep should a fish-only saltwater tank be?

I would recommend a depth of at least 24 inches for a fish-only tank, although a 30 inch depth would be more ideal in my opinion. Not only would this increase the overall water volume but it would also create more swimming room for the fish above the rockwork which more closely mimics their natural habitat. Read more about Aquarium Tank Size | Length, Width and Height

2. How do I control salt creep in a saltwater tank?

Salt creep is harmless and is a by-product of droplets of saltwater splashing from the water’s surface due to surface agitation from powerheads and return pumps. If your powerheads are aimed at too much of an angle towards the surface of the water, it will cause an increase in evaporation as well as salt creep because of the droplets of water bouncing off the surface. Remember, however, that a reasonable amount of surface agitation is a good thing as it allows for efficient gas exchange which maintains oxygen levels in the water.

Salt creep is only a nuisance when it gets onto your light fixtures, impeding the maximum amount of light from reaching your corals. The best way to control salt creep is to wipe it off with a damp cloth every 2 weeks or so. Make sure to turn off your light fixtures at the mains before taking a wet rag to them!

3. Are acrylic aquariums good?

It depends on what you mean by ‘good’. Acrylic aquariums are much stronger and resistant to leaks which is why you will always find very large public aquariums use acrylic rather than glass for their displays. And since acrylic is also able to ‘flex’ much more than glass, it will not crack or shatter like glass can.

The downside to acrylic is that it scratches easily. A grain of sand lodged in a typical cleaner magnet can cause long scratches when the magnet is pulled across the viewing surface.

Scratches that occur on the inside of the tank and underwater are permanent, unless you’re willing to drain the tank to buff them out with an acrylic polishing compound — not an option unless you’ve given up the hobby and are selling off your empty acrylic tank. In my opinion, acrylic tanks are too much trouble to keep scratch-free and will require a daily cleaning regimen to keep stubborn algae from building up. Read more about acrylic on Ready-Made Aquariums

4. What type of silicone should be used when constructing a saltwater aquarium?

An established and reputable custom tank builder will always use silicone that is meant for aquarium construction. If you are attempting to build a tank yourself — and I don’t recommend that you do unless you are particularly experienced in this field — then using an appropriate type silicone is very important. Using the wrong type of silicone will lead to the tank leaking in the very near future. Or worse. Not all silicone is created equal!

Some silicon is meant for weather insulation, and while waterproof, is not intended for aquarium construction.

You also do not want to use any silicone that has mould or mildew inhibiting chemicals in it as they could poison your livestock. On the other hand, there are silicones that are FDA approved and Food Grade.

Momentive RTV Silicones RTV103 and RTV108 are commonly used for aquarium building but since specifications can change, I would recommend checking with the manufacturer directly.

5. Can bio-balls be used in a reef tank?

Bio-balls came from the era of wet/dry filters. Water from the aquarium was allowed to trickle over a sump or overflow chamber filled with bio-balls. The bio-balls were not submerged and the constant mixture of water and air over the bio-balls caused aerobic bacteria to flourish. Aerobic, oxygen-loving bacteria which consumed deadly ammonia and nitrite lived on the surfaces of the bio-balls. In this way, ammonia and nitrite were efficiently converted to nitrate which was far more tolerable to fish.

But since anaerobic bacteria, the ones which thrived only in oxygen-poor zones and which consume nitrate, were totally left out of the wet/dry filter equation, nitrate levels rose, giving way to the term ‘nitrate factory’. Indeed, ‘wet/dry filters’ and ‘nitrate factory’ became almost interchangeable terms! This is also the reason why bio-balls fell out of favour with the advent of reef aquariums where nitrate needed to be kept at low levels so that corals could survive.

But you CAN still use bio-balls as a biological filter medium in a reef aquarium without the nitrate issues. This is accomplished by simply ensuring that the bio-balls are completely submerged in an area of the sump so that anaerobic bacteria can find a home in them. Care should be taken during routine maintenance to not rinse out all the bio-balls at once so as not to impact the aquarium’s biological filter.

Read about The Nitrogen Cycle to understand more about aerobic and anaerobic bacteria.

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