D - Aquarium Dictionary

Updated August 12, 2019
Author: Mike - FishLore Admin
Social Media: FishLore on Social Media

Aquarium Fish Definition and Glossary

Daphnia :
is also known as water fleas, this is a nutritious fish food that is found in lakes and streams. More here:
Daphnia on Amazon

Dechlorinator :
a water additive used to eliminate chlorine and sometimes chloramine from tap water. This product is used when adding new water to the aquarium since chlorine and chloramine can harm fish. One of the most popular dechlorinators is Seachem Prime on Amazon because it detoxifies ammonia, nitrites and nitrates. See:
Prime on Amazon

Deionization :
is the process of removing ions from a solution (water) using an ion exchange resin. Sometimes used in conjunction with a Reverse Osmosis water filter to remove impurities from tap water before using it in the aquarium.

Denitrification :
is a process where nitrates are converted to harmless nitrogen gas that escapes at the tank water surface. In order for this process to take place there needs to be anoxic or anaerobic conditions in the aquarium. These anoxic or anaerobic places are usually found in the lower layers of Deep Sand Beds and deep within Live Rock.

Detritus :
is decomposing organic materials, but you can also think of it as fish waste or uneaten fish food that settles into or on the substrate.

Detrivore :
organisms (fish and invertebrates) that eat detritus.

Diatomaceous Earth :
a very soft rock made out of fossilized diatom algae that is crumbled into a powder for use in diatom filters.

abbreviation for Drs. Foster and Smith which is an online aquarium and pet supplies website.

DG :
short for Dwarf Gourami.

DI :
abbreviation for DeIonization. Also see: Reverse Osmosis and Deionization.

Diapause :
usually used in reference to insects, but in our case the killifish. The embryos of killifish can go through a stage of suspended growth or development called diapause.

Diatom Filter :
a mechanical filter that pushes or pulls the tank water through packed diatomaceous earth material which cleans the water, or polishes the water. They can become clogged quickly and are usually only used occasionally to polish aquarium water.

Discus :
is a type of freshwater fish. Also see the Discus profile page.

Dinoflagellate :
is also known as saltwater plankton. Some are photosynthetic and these are called zooxanthellae.

Dissolved Oxygen :
is the amount of oxygen dissolved in the aquarium water for use by the tank inhabitants. It is measured as a saturation level or in ppm. Fish need oxygen in the water for respiration.

Distilled Water :
the distilling of water is the process where water is heated to a boil, the water vapors (steam) are collected in tubes where they cool and drip into another clean container. Distilled water could be considered pure water in that it removes many dissolved solids, salts and organics. Distillers can sometimes be a pain to clean and it's usually easier to generate pure water using reverse osmosis and deionization. Saltwater aquarium or reef tank keepers may be interested in reverse osmosis units.

Dither Fish :
these are fish that stay out in the open all the time and in the process will calm and reassure more reclusive fish species that it's safe for them to venture out from their hiding spot.

Diurnal :
is a plant, animal or fish that is active during the daytime.

abbreviation for Do It Yourself. There are many pieces of equipment that hobbyists like to make on their own. For instance, here is a DIY Homemade Algae Scraper.

dKH :
abbreviation for Degrees of Carbonate Hardness and is a measurement of total alkalinity. Use a test kit to measure it, like the following:
GH/KH Test Kit on Amazon

abbreviation for Dissolved Organic Carbon or Dissolved Organic Compounds. DOC is the dissolved carbon compounds in the aquarium water that form as a result of various biological processes that take place in the aquarium. It's difficult to measure DOC in aquariums, so Nitrate was one of the things hobbyists started to use as a guide to know when the DOC's were getting too high. When the nitrates started edging up so too were the dissolved organics. To remove DOC from your aquarium you will need to do water changes, use chemical filtration and protein skimming in saltwater aquariums.

Dolomite :
is a carbonate rock composed of calcium magnesium carbonate. Saltwater hobbyists sometimes use this material as a substrate but it takes a lower pH than aragonite to dissolve and may therefore not be as suitable for a marine substrate as aragonite.

Dorsal Fin :
the fin located on top of the fish. Some fish even have two dorsal fins. Also see: Fish Anatomy.

Dosing Pump :
is a pump used to regulate and administer a slow dose or drip to the aquarium on a continuous or ocassional basis. Kalkwasser is somtimes dosed using a slow drip dosing pump. See:
Dosing Pump
Dosing Pump on Amazon

Drip Acclimation :
a procees used to acclimate fish, coral, plants or invertebrates to your aquarium water. Drip acclimation is a much slower process than other fish acclimation methods but it is also safer and better for what you are acclimating. It's basically a slow and steady drip, drop by drop, of the tank water into the holding container over the period of an hour or more. This process slowly acclimates the fish to the pH, temperature, alkalinity, dissolved organics and oxygen levels in a methodical manner. You can get a drip acclimation kit to make it easier. See below:
Drip Acclimate
Drip Kit on Amazon

Driftwood :
are old tree branches that are used in aquariums for decoration. It is important to sterilize or "cure" the driftwood before using it in your tank. You can boil it (for a couple of hours) or simply let it soak in an aquarium use only bucket for several weeks. Boiling is quicker and you can usually get it ready after a few hours of boiling. Driftwood will release tannins that can soften the water and also cause a drop in pH. See:
Driftwood on Amazon

Dropsy :
is an accumulation of fluids in the tissues of fish, making the fish appear bloated or the scales to stick out. This is thought to be caused by a bacterial infection brought about by poor aquarium husbandry (dirty water) and improper diets. Also see: Fish Disease.

an abbreviation for Deep Sand Bed. Deep Sand Beds are used in saltwater aquariums for the purpose of denitrification.

Duckweed :
an aquarium plant that is considered hardy with low to moderate lighting requirements.
Duckweed on Amazon

Dwarf Hairgrass :
a very popular aquarium plant that is used to carpet the tank. It looks amazing once grown out. See:
Dwarf Hairgrass
Dwarf Hairgrass on Amazon

Dwarf Sagittaria :
an aquarium plant often used in the foreground in larger aquariums. Considered a fairly hardy starter plant.
Dwarf Sag
Dwarf Sag on Amazon