Aquarium Fish

P - Aquarium Dictionary

Aquarium Fish Definition and Glossary

abbreviation for Photosynthetically Active Radiation. It is the amount of light that is available at depth for corals, plants and other photosynthetic organisms. It is important to know how much PAR your light fixture puts out so you can know what types of light demanding corals you can keep and/or where to place them depth wise in your tank. You can measure PAR using a meter:
PAR Meter
PAR Meter

Paraguard :
is an aquarium medicine made by Seachem used to treat parasites on fish. Used to eradicate many ectoparasites (ich) and external fungal, bacterial, and viral lesions (fin rot).

Parasite :
is an organism that lives on or in another organism and benefits by stealing nutrients at the host organism's expense. Fish can get parasites with the most common being ICH. You can use Paraguard to treat parasites in fish.

Parasitism :
a form of symbiosis in which one organism benefits from the association and the other organism is harmed.

PC :
abbreviation for Power Compact and refers to Power Compact fluorescent lights.

Pelagic :
for our purposes, this term is usually used when referring to the breeding styles of many marine species. These species essentially release the fertilized eggs into the open ocean to be carried by the currents. This breeding style can be quite difficult for breeders to successfully raise larvae.

PFS - Pool Filter Sand :
is sand that is used in aquariums sometimes because it is cheaper than other types of sand. More info on Pool Filter Sand

pH :
this is a water measurement on a logarithmic scale that will tell you if your water is considered acidic, neutral or alkaline. A pH of 7 is considered "neutral", under 7 is considered "acidic" and over 7 is considered "alkaline". Get a pH test kit to measure the pH of your aquarium:
pH Test Kit

Phosban :
is an aquarium product made by the company Two Little Fishies and is used to remove phosphate from aquarium water. These are ferric oxide hydroxide granules with an extremely high capacity for adsorbing phosphate from saltwater and freshwater. Also adsorbs silicate and does not release adsorbed substances. This is best used in a TLF media reactor. Get phosban below:

Phosguard :
an aquarium product made by Seachem that is used to remove phosphates and silicates from aquarium water. Phosphates and silicates in tank water can lead to nuisance algae blooms. You can run it in a media reactor or place a bag of it in your sump, although you will get much better results running it in a reactor. 100 milliliters treats 60 US gallons. See:

Phosphate :
PO4, consists of Phosphorous and Oxygen, is a primary ingredient for algae. Aquarists should try to limit phosphates in the aquarium water to prevent noxious algae blooms. Get a phosphate test kit to test your tank water:
Phosphate Test Kit
PO4 Test Kit

PimaFix :
a freshwater and saltwater fish medication made by API and is used to treat fungal and bacterial infections in fish. API claims that it alleviates symptoms like fungus or cotton like growths on fins, mouth and body. Safe to use in reef tanks and will not harm the biological filter. Use 5ml per 10 gallons of aquarium water.

Piscinoodinium :
the freshwater version of the parasitic single cell organism in velvet disease.

Pleco :
is a type of freshwater fish. Also known as the Plecostomus. See the Pleco profile page for more information on this species.

Plenum :
mostly used only in saltwater aquariums, this is an open space under a deep sand bed that is used to promote biological filtration in the sand bed.

Power Compact Light :
is a U shaped fluorescent light that is able to generate more light than standard fluorescent tubes. Power compacts are reported to be more energy efficient while producing more light intensity. They can be a viable alternative for smaller and shallow saltwater reef tanks. They do put off some heat and a fan may be needed. They range anywhere from 9 watts through 96 watts.

Power Filter :
an HOB aquarium filter that performs mechanical filtration, biological filtration and chemical filtration. It performs mechanical filtration by pulling in tank water and forcing it through filter floss. Chemical filtration is accomplished by using activated carbon inside the filter floss. The better power filters also have a course media that the water flows through as it exits the power filter. This course media is a colonizing area for the beneficial bacteria that perform biological filtration. These aquarium filters are very popular because they are inexpensive, easy to maintain and do a decent job. It is important to replace the filter floss (not the bio-filter) when needed to prevent nitrates from accumulating in the filter.
Power Filter
Power Filter

power head :
is aquarium equipment that is used to perform water movement inside the aquarium. power heads can be great if you don't want to run plumbing lines to an external water pump. power heads are also sometimes used with a UGF to create a reverse flow undergravel filter. There are some drawbacks to using power heads inside your aquarium. They can add heat and using several can be a problem if tank temperature is staying too high. The water intake strainer needs to be cleaned on a regular basis to perform at peak efficiency and having several in a tank can be a bit distracting and take away from the beauty of a tank (personal opinion of course). For more details on powerheads, go here

Parts Per Million, is a unit of measurment used in many test kits and is equivalent to mg/L.

Prazipro :
a medication for freshwater, saltwater and pond fish that treats disease conditions such as flukes, flatworm and turbellarians. 5 percent praziquantel by weight.

Prime :
an extremely popular water supplement that helps with the slime coat on fish, removes chlorine and chloramine and detoxifies ammonia, nitrite and nitrate.

Pristine :
aquarium supplement made by Seachem that contains bacteria that breaks down detritus, excess food and sludge in both freshwater and saltwater aquariums. It is also supposed to reduce excess nutrients (e.g. ammonia, nitrites and nitrates). Used to increase water clarity and better health in your aquarium.

Protein Skimmer :
a saltwater aquarium filtration device used to remove dissolved organics from the water using a process called foam fractionation. The protein skimmer pulls in water from the fish tank and then agitates it thereby forming tiny microbubbles. These tiny microbubbles attract the dissolved organics on the bubble surface. As these bubbles accumulate they are slowly forced upwards into a skimmer collection cup. Frequent maintenance is vital for the proper operation of a protein skimmer. The collection cup, the riser tube the bubbles travel up through and the water intake into the skimmer should be cleaned frequently to keep the skimmer operating a peak capacity. Protein skimmers help by removing these dissolved organics before they have a chance to turn into nitrates. If these dissolved organics are not removed from the water column they can cause problems such as nuisance algae growth, yellowing of the water, and an overtaxed biological filter.

Protogynous Hermaphrodite :
when a species begins life as a female and changes to a male. Often only a one way change, (i.e they can't change back to female) that can be triggered by the death of the lead male in the harem, the dominant female will turn into a male. The change process can take weeks to months to complete.

Pulsing Xenia :
see Pulsing Xenia for detailed information - a coral with polyps that pulse.

Purigen :
an aquarium product made by Seachem that removes impurities from aquarium water. Purigen controls ammonia, nitrites and nitrates by removing nitrogenous organic waste before it breaks down in the tank. It does have a minimal impact on trace elements. It claims to significantly raise redox. Purigen darkens as it exhausts, and is easily renewed by treating with bleach. Purigen is designed for both marine and freshwater use.

Poly Vinyl Chloride, is a hard plastic type material used in plumbing aquariums and for routing water throughout multiple systems.

abbreviation for Partial Water Change. More info on aquarium maintenance.

Python Water Changer :
this is aquarium equipment designed to make it easier and quicker to do partial water changes. It hooks up to your faucet and will remove old water and then refill with new tap water. You have to treat the water as it is added to your tank with prime or similiar. Make sure the temperature is as close as possible to the tank water too to prevent stressing out the fish!
Python Water Changer

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