Understanding Your Fish Tank Water Hardness

            We have all seen the instructions on testing kits that tell us how to test for certain chemicals in the tank but sometimes we are not exactly sure what we are testing and why. In this article I will cover the two basic types of water hardness which are General Hardness (GH) and Carbonate Hardness (KH).

            General Hardness (GH) is a test that measures the amount of Calcium (Ca²⁺) and Magnesium (Mg²⁺) that has dissolved in your freshwater tank. Hard water, testing at > 200 ppm, is high in both Calcium and Magnesium. Soft water, testing between 50-100 ppm is low in these minerals. It is important to know that a special saltwater test is required for saltwater aquariums because the ions of Calcium and Magnesium are higher than the testing ranges for most test.

            The general hardness of your tank can increase over time and so it is important to check the water level continuously. As water evaporates it leaves behind the metal elements which increase the general hardness, when water is added more metals are added to the tank further increasing the hardness. Adjusting the level of your water hardness can be as simple as completing partial water changes using deionized water or adding a water softener “pillow” to the filter to reduce the hardness, or by using specialized salt to increase the hardness.

            Different types of fish require certain hardness levels and the following is small listing of fish and some plants along with their hardness requirements.

30ppm- Discus, arowanas, elephant nose, neons and cardinals.

60ppm- Certain Tropical fish, angelfish, tetras, botia, and community aquariums.

120ppm- Certain Tropical fish, swordtails, guppies, mollies, cichlids and certain goldfish.

180ppm- African Cichlids and certain goldfish.

            Carbonate Hardness (KH) is also known as Alkalinity and is the measure of Carbonate (CO₃²) and Bicarbonate (HCO₃). This type of hardness helps to stabilize the pH in your aquarium and with a high level (> 200ppm) your aquarium will have a high pH. In low levels, your tank water will be acidic and you will experience rapid shifts in pH. Carbonate is used by aquarium plants and consumed in the filter so this level will need to be maintained or it will fall and become unstable.

           Reducing you Carbonate Hardness is as simple as doing a partial water change and using distilled or deionized water. Increasing can be done by using a pH adjuster

            The following are acceptable levels for the listed fish. Please check the levels for your individual fish.

40ppm- Discus, arowanas, elephant nose, neons and cardinals.

80ppm- Certain Tropical fish, angelfish, tetras, botia, and community aquariums.

120ppm- Certain Tropical fish, swordtails, guppies, mollies, cichlids and certain goldfish.

180ppm- African Cichlids, certain goldfish brackish water and certain marine fish.

240ppm- Rift Lake Cichlids, certain goldfish, brackish water and certain marine fish.

Squirrelfish

• Should be kept in a tank of at least 70 gallons. These fish range in size but they are usually between 7 inches and 1 foot.
• These are peaceful fish.
• Will eat meaty foods.
• Place in reef tanks with caution.
• CAUTION SHOULD BE USED WITH THESE FISH. CERTAIN TYPES ARE VENEMOUS.

Water conditions should be:      Temperature: between 72 and 78 F

                                                dKH: 8-12

                                                pH: 8.1-8.4

                                                sg: 1.020-1.025

Squirrelfish compatibility-

Caution should be used when placing Squirrelfish with Blennies, Butterflies, Cardinals, Chromis, Damsels, Dartfish, Dragonets, Eels, Gobies, Jawfish, Hogfish, Lions/Scorpions, Sharks/ Rays, Triggerfish, Wrasse and Invertebrates.

Extreme Caution: Squirrelfish should not be placed in a tank with Groupers and Seahorse/Pipefish.

Triggerfish

• Should be kept in a tank of at least 70 gallons with larger species needing tanks of 150 gallons or more. These fish range in size but are usually between 7 and 18 inches.
• These are generally aggressive fish.
• Will eat meaty foods.
• These fish are not reef compatible.

Water conditions should be:      Temperature: between 72 and 78 F

                                                dKH: 8-12

                                                pH: 8.1-8.4

                                                sg: 1.020-1.025

Triggerfish compatibility-

Caution should be used when placing Triggerfish with other Triggerfish Dwarf Angles, Large Angles, Anthias, Blennies, Boxfish, Butterflies, Chromis, Clownfish, Damsels, Eels, Foxface/Rabbits, Gobies, Groupers, Grunts/Sweetlips, Jawfish, Hawkfish, Hogfish, Lions/Scorpions, Parrotfish, Puffers, Squirrelfish, Tangs/Surgeons, Triggerfish, Wrasse and live corals.

Extreme Caution: Triggerfish should not be placed in a tank with Anglers/Frogs, Bassles, Batfish, Cardinals, Dartfish, Dragonets, Filefish, Pseudochromis, Seahorse/Pipefish, Sharks/Rays and Invertebrates.

Puffers

• Should be kept in a tank of at least 30 gallons with larger species needing up to 70 gallons. These fish range in size but are usually around 8 inches in size with a few types reaching 10 or more inches.
• These fish are semi-aggressive.
• Will eat meaty foods.
• These fish are not reef compatible.

Water conditions should be:      Temperature: between 72 and 78 F

                                                dKH: 8-12

                                                pH: 8.1-8.4

                                                sg: 1.021-1.025

These fish difficult to care for and range in pattern and colors depending on the type that you get. Some species have spines while others have unique color patterns.

Puffers compatibility-

Caution should be used when placing Puffers with Anglers and Frogs, Basslets, Boxfish, Dartfish, Groupers, Pseudochromis, Triggerfish, and Wrasse.

Extreme Caution:  Puffers should not be placed in a tank with other Puffers, Seahorse/Pipefish, Sharks and Rays and Invertebrates.

Seahorses

• Should be kept in a tank of at least 30 gallons. These fish range in size but they are usually between 4 and 6 inches.
• These are peaceful fish.
• Will eat meaty foods.
• Are reef friendly

Water conditions should be:      Temperature: between 72 and 78 F

                                                dKH: 8-12

                                                pH: 8.1-8.4

                                                sg: 1.020-1.025

These fish are easily recognized by their odd shaped bodies and long tails. Seahorses are Moderate in care level.

Seahorse  compatibility-

Caution should be used when placing Seahorses with Dartfish, Gobies, Jawfish and Invertebrates.

Extreme Caution: Seahorse should not be placed in a tank with Dwarf Angles, Large Angles, Anglers/Frogs, Anthias, Basslets, Batfish, Blennies, Boxfish, Butterflies, Cardinals, Chromis, Clownfish, Damsels, Eels, Filefish, Foxface/Rabbits, Groupers, Grunts/Sweetlips, Hawkfish, Hogfish, Lions/Scorpionfish, Parrotfish, Pseudochromis, Puffers, Sharks/Rays, Squirrelfish, Tangs/Surgeons, Triggerfish, and Wrasse.

Pseudochromis

• Should be kept in a tank of at least 30 gallons. These fish range in size but are usually around 4 inches in size.
• These fish are semi-aggressive.
• Will eat meaty foods.
• These fish are reef compatible.

Water conditions should be:      Temperature: between 72 and 78 F

                                                dKH: 8-12

                                                pH: 8.1-8.4

                                                sg: 1.021-1.025

These fish are generally easy to care for and range in pattern and colors depending on the type that you get. Typically these fish are bright neon colors.

Pseudochromis compatibility-

Caution should be used when placing Pseudochromis with Large Angels, Batfish, Blennies, Cardinals, Dartfish, Dragonets, Filefish, Hogfish, Parrotfish, Puffers, and Wrasse.

Extreme Caution:  Pseudochromis should not be placed in a tank with other Pseudochromis, Anglers and Frogs, Basslets, Eels, Groupers, Lions and Scorpions, Seahorse/Pipefish, Sharks and Rays and Triggerfish.

Lionfish

• Should be kept in a tank of at least 50 gallons. These fish range in size but can reach over 1 foot in size.
• These fish are semi-aggressive.
• Will eat meaty foods.
• Place these fish in reef tanks with caution.
• USE EXTREME CAUTION. THESE FISH ARE VENOMOUS.

Water conditions should be:      Temperature: between 72 and 78 F

                                                dKH: 8-12

                                                pH: 8.1-8.4

                                                sg: 1.021-1.025

These fish are Moderate in care level. Lionfish range in pattern and colors depending on the type that you get.

Lionfish compatibility-

Caution should be used when placing Lionfish with Dwarf Angels, Anthias, Batfish, Butterflies, Filefish, Grunts/Sweetlips, Hogfish, Parrotfish, Sharks and Rays, Squirrelfish, Triggerfish, Wrasse, and Invertebrates.

Extreme Caution:  Lionfish should not be placed in a tank with Basslets, Blennies, Cardinals, Chromis, Clownfish, Damsels, Dartfish, Dragonets, Gobies, Jawfish, Hawkfish, Pseudochromis, Seahorse/Pipefish

Hogfish

• Should be kept in a tank of at least 150 gallons. These fish range in size but are generally around 10 inches.
• These fish range from peaceful to aggressive.
• Will eat meaty foods.
• Place these fish in reef tanks with caution. Some species will be ok with reefs as juveniles but are not ok as adults

Water conditions should be:      Temperature: between 72 and 78 F

                                                dKH: 8-12

                                                pH: 8.1-8.4

                                                sg: 1.020-1.025

These fish are Easy to Moderate in care level. Hogfish range in pattern and colors depending on the type that you get.

Hogfish compatibility-

Caution should be used when placing Hogfish with Anglers and Frogs, Basslets, Batfish, Blennies, Cardinals, Chromis, Clownfish, Damsels, Dartfish, Dragonets, Eels, Gobies, Groupers, Jawfish,  Lions/Scorpionfish, Pseudochromis,  Sharks and Rays, Squirrelfish, Triggerfish, Wrasse and Invertebrates.

Extreme Caution:  Hogfish should not be placed in a tank with other Hogfish and Seahorse/Pipefish.

Hawkfish

• Should be kept in a tank of at least 30 gallons. These fish range in size but are generally around 3 inches.
• These fish range from peaceful to aggressive.
• Will eat meaty foods.
• Place these fish in reef tanks with caution.

Water conditions should be:      Temperature: between 72 and 78 F

                                                dKH: 8-12

                                                pH: 8.1-8.4

                                                sg: 1.020-1.025

These fish are Easy in care level. Hawkfish range in pattern and colors depending on the type that you get but all will add a great splash of color to your aquarium.

Hawkfish compatibility-

Caution should be used when placing Hawkfish with other Hawkfish, Anglers and Frogs, Boxfish, Grunts/Sweetlips, Triggerfish, Wrasse and Invertebrates.

Extreme Caution:  Hawkfish should not be placed in a tank with Eels, Groupers, Lions/Scorpionfish, Seahorse/Pipefish and Sharks and Rays.

Jawfish

• Should be kept in a tank of at least 30 gallons. These fish range in size but are generally around 3 inches.
• These fish are usually peaceful with certain breed being semi-aggressive.
• Will eat meaty foods.
• These fish are reef compatible.

Water conditions should be:      Temperature: between 72 and 78 F

                                                dKH: 8-12

                                                pH: 8.1-8.4

                                                sg: 1.021-1.023

These fish are Moderate in care level. Jawfish range in pattern and colors depending on the type that you get.

Jawfish compatibility-

Caution should be used when placing Jawfish with other Jawfish, Large Angels, Blennies, Chromis, Grunts/Sweetlips, Hogfish, Parrotfish, Seahorse/Pipefish, Squirrelfish, Triggerfish and Wrasse.

Extreme Caution:  Jawfish should not be placed in a tank with Anglers/Frogs, Eels, Groupers, Lions/Scorpionfish, Sharks and Rays.