H - Aquarium Dictionary

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

Aquarium Fish Definition and Glossary

Habitat :
is the location where an animal, plant or fish naturally lives. It can be important to understand the natural habitats of the animals we keep in order to try and replicate them in the aquarium.

Hard Water :
is water that contains many minerals, such as calcium and magnesium. When you have hard water (use a test kit) it can be more difficult to regulate the aquarium pH. Reverse Osmosis filters can soften hard water. Some fish species (like many tetras) do better in softer water.

Heater :
is aquarium equipment that is used to increase or maintain the temperature of the aquarium water. There are many types and varieties of aquarium heaters on the market and it can be a good idea to invest in two lower wattage heaters instead of one higher wattage heater in case of heater malfunctions. See below:
Aquarium Heaters on Amazon

Heat Pack :
is used when transporting or shipping aquarium livestock that helps keep the bag water at a steady temperature while shipping. These are especially important to use when shipping livestock to colder climates. Different heat packs have different ratings on how long they will provide heat. They can mean the difference between life and death. More below:
Heat Pack
Heat Packs on Amazon

Herbivore :
is a fish that mainly eats plants, algae, or plant matter.

Hermatypic :
usually used in reference to corals, it means that the coral has the symbiotic algae zooxanthellae present in their tissue. Hermatypic corals depend on photosynthesis for the majority of their nutrients and appropriate lighting is vital for the proper care of these animals.

abbreviation for High Intensity Discharge and refers to high intensity lights such as metal halide lights.

Hermaphrodite :
is a fish or other animal that has both male and female organs for producing eggs and sperm.

Hexamita :
is a parasite that lives in the intestines of fish. You can treat/prevent it with medicated foods such as Hex Shield:
Hex Shield
Hex Shield on Amazon

abbreviation for Hole In The Head, which is a fish disease. Read more on this fish disease here: Fish Disease.

HO Light :
refers to High Output fluorescent aquarium light. HO lighting is gaining in popularity as an economical method for placing high intensity lighting over reef tanks while not adding much heat to the tank water. HO lamps are usually in the 20-60 watt range, sometimes higher. T5 lights are considered HO lights. HO lights may not be as intense as VHO bulbs or Metal Halide bulbs.

abbreviation for "Hang on Back" and refers to aquarium equipment that can hang on the back of the tank. Most aquarium products will list in the product description whether or not they are HOB. HOB equipment eliminates the need for running your own plumbing lines outside the aquarium but the downside is that you can easily see the equipment hanging on the back of the tank. See below:
HOB Filter
HOB Filter on Amazon

Holey Rock :
also known as "Texas Holey Rock" or Honeycomb limestone, is rock with lots of weathered holes that looks quite dramatic in a fish tank and is actually functional too because fish like to hide and swim through the holes. More here:
Holey Rock
Holey Rock on Amazon

Hospital Tank :
very similar to and sometimes synonymous with a quarantine tank. A hospital tank is a bare bones setup that is used for treating sick or diseased fish. They usually have a filtration system, no substrate, a heater, some place for the fish to hide (pvc tube maybe), lights and thats about it. The sick fish are held in the hospital tank while they are treated for the infection or disease and once they recover they are released back into the main tank.

an abbreviation for High Quartz Iodide and is used when referring to metal halid bulbs. HQI can be in either the single ended or double ended metal halide varieties. The HQI bulbs supposedly burn brighter, with more intensity than standard metal halide bulbs.

Hybrid Fish :
is a fish that is a cross between two different fish species. There is much controversy and many ethical issues around the inter-breeding of different fish species.

Hydor Theo :
is a heater line from Hydor. These are submersible heaters that range in power from 25 watts up to 200 watts. They can be positioned vertically or horizontally inside the tank or sump. See:
Hydor Theo
Hydor Theo on Amazon

Hydrometer :
is a device used to measure the specific gravity of the aquarium water. Brackish tank and saltwater tank keepers need this device to monitor specific gravity levels. See:
Hydrometer on Amazon