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Three Rules of Thumb and Why You Shouldn't Use Them

Three Rules of Thumb and Why You Shouldn't Use Them

Postby hegi on Mon Oct 12, 2009 6:52 pm

I think one of the things that a lot of new reef aquarists latch onto when they first start out are three "______ per gallon" rules of thumb that can hinder their progress or actually be harmful to the overall health of their tank. The three rules of thumb I'm referring to are: (1) Watts per Gallon); (2) Lbs of LR per Gallon; and (3) Inches per Gallon.

All three of these rules, in my opinion, are the result of the early years of reef-keeping in the late 80s and early 90s (I bought my first reef in 1994) when we didn't completely understand what was necessary to be successful in creating reefs in small, closed systems. Despite our progress in both understanding the science of reef aquariums as well as the advancements in filtration systems, lighting, etc., these three seem to remain well-entrenched in some hobbyists' minds. Furthermore, all three were/are often part of the advice new hobbyists receive from LFSs or others when they are contemplating diving into the hobby.

The first is the old "watts per gallon" myth. The myth is applied when discussing which lighting setup is appropriate for keeping different kinds of livestock. For example, you might be told it is necessary to have a much higher amount of watts per gallon to keep certain SPS or clams where you can get away with much less in order to keep soft corals. The problem with the watts per gallon myth is that it does not take into account the quality of the light you are providing. All lighting is not created equal. You may have 500 watts of CFL lighting but that doesn't mean you'll be able to keep that frag of Sunset Montipora or Superman Montipora alive. Even if you can don't count on it keeping its vibrant colors. If, on the other hand, you have a 150 Watt Metal Halide pendant, you can keep such a coral and it will even thrive as long as you're water quality and flow are in check as well. So even though the halide setup is providing 350 watts less than the CFL setup it is actually providing more PAR [Photosynthetically Available Radium], which is what the algae present in the corals' tissue are using to produce energy and feed the coral itself. Think about what kind of animals you want to keep in the long term before making the investment in a lighting system. It is one of the most expensive and important parts of your system. Believe me, for most people it is only a matter of time before colorful SPS corals or clams catch your eye and force you to come to terms with the fact that you have a CFL fixture that doesn't provide the light necessary to keep them, which results in another purchase.

Second, Lbs of Live Rock per Gallon. Often we are told that it is necessary to keep at least 1 to 2 lbs of live rock per gallon of aquarium capacity in order to establish a working filter for our reefs. This is completely misleading. The ability of live rock to act as a natural filter, and the primary filter that will keep your reef's water clean, is dependent on the surface area of the rock itself, which is also related to how porous it is. Lets say you purchase 40 lbs of limestone or other dense "base rock" to fill your 40 gallon aquarium thinking you are fulfilling the 1 lbs per gallon rule. This rock can be encrusted in coraline algae and be well-aged but it is not providing you with the same filtering ability as say 10 or even 5 lbs of Fiji or Tonga rock. In the latter case your actually providing a much better filter for your system by purchasing less because it has much more surface area for denitrifying bacteria to inhabit and is also full of other creatures that will help you maintain a biological diverse and clean ecosystem.

Finally, the inch per gallon rule. The inch per gallon rule is another misnomer transferred from the freshwater hobby. It states, "you can have X number of inches of fish per gallon of aquarium capacity." The problem with this rule is it does not take into account most of the needs of the fish you are buying. Many fish, such as tangs, need a lot of swimming room, and cannot/will not thrive in very small systems. Say a LFS employee or another hobbyist tells you to stick to 2 inches of fish per gallon of aquarium water. You have a 20 gallon aquarium. "This is great!" you think, "That yellow tang I wanted is only 10 inches long! I still have 30 inches of fish left to buy!" Obviously this is an extreme example, but suffice it to say a 10-inch tang will definitely not be as excited about finding him or herself in your 20 gallon aquarium as you are to see it there. Another important factor is territoriality of fish. You may be able to fit five or six clown fish in a 40-50 gallon aquarium but there probably won't be five or six clowns left a few weeks or months down the road.

Hopefully this will be helpful to some people who are starting out in the hobby. There is a lot of unintentional misinformation out there that is the result of ignorance rather than malice and it is important to read a lot and educate yourself fully before making livestock or equipment purchases. Always try to have a end goal for your system and keep the well-being of your future wards in mind as well before purchasing them.
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Re: Three Rules of Thumb and Why You Shouldn't Use Them

Postby Reefmike on Mon Oct 12, 2009 9:11 pm

Thought this would make a good sticky for the top of this forum.
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Re: Three Rules of Thumb and Why You Shouldn't Use Them

Postby Aquatic Therapy on Tue Nov 03, 2009 9:56 am

Very nice write up!
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Re: Three Rules of Thumb and Why You Shouldn't Use Them

Postby Jeff on Tue Nov 03, 2009 11:23 am

Also a good article for the newsletter.
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Re: Three Rules of Thumb and Why You Shouldn't Use Them

Postby fishyjoe24 on Mon Jan 03, 2011 5:01 am

Thanks, that really helped me out as I had a saltwater tank for a short while and would like to get back in to saltwater and lost a of what I know when I sold it and went back to freshwater.....
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Re: Three Rules of Thumb and Why You Shouldn't Use Them

Postby BrianG on Thu Feb 10, 2011 5:45 am

Very well written!!
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Re: Three Rules of Thumb and Why You Shouldn't Use Them

Postby Llawen on Mon Jul 04, 2011 8:35 am

Well done, and the inches per gallon thing erks me to the bone. But those that "think" they know and follow that rule always are having fish dying. Our systems heal themselves if needed. By, killing a fish to eae the burdon on the ecosystem in the tank, and the foolish part is: I see and hear them crying about the loss of their fish and off to get another one. No two ecosystems are the same, and MUST be approached with this thinking to have a successful saltwater/freshwater or reef aquarium.
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