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Change half the water when either ammonia or nitrite approach 0.50ppm (alternately, 25% at 0.25ppm), or weekly, whichever comes first. Add Seachem Prime at 2-drops per gallon of tank size every day until cycled.

That’s all you have to do. You can stop reading now. But there’s a lot of information packed into that sentence. So let’s go over it again – slowly.

Change half the water...

Removing water is most easily done with a siphon; also known as a gravel vacuum. Although a clean, new turkey baster will also work. Suck up as much old food, plant debris and feces as you can conveniently. Replace with water of the same temperature (within a few degrees either way). Add the Prime to the tank just before refilling. You don’t have to “age” the water except in special conditions. See pH matching – below.

when either ammonia or nitrite approach 0.25-0.50ppm...

You need a water test kit to get these readings. Liquid tests are considered more consistently accurate than test strips, and they are cheaper per test. Most fish-keepers use the API master test kit ( which contains the tests you need. Test every day until you learn how fast ammonia builds up in your tank. (ppm is parts per million.)

You also need a filter to cycle a tank. Cycling bacteria need oxygen and water flow. A filter is the best and easiest way to provide both. Do not rinse or replace the filter during the cycle.

or weekly, whichever comes first...

A weekly 25%-50% water change with vacuuming is part of recommended tank maintenance. If ammonia and nitrite stay below 0.25-0.50ppm the tank goes onto the weekly water-change schedule.

add Seachem Prime at 2-drops per gallon of tank size every day...

This is IMPORTANT: Prime water conditioner (by Seachem) allows you to have a little ammonia or nitrite in the tank without endangering your fish. This protection goes away within 48 hours so it’s necessary to add more Prime. Seachem recommends 2 drop/gal of tank size with water changes. A further dose of 2-drops/gal every day keeps the protection fresh.

Other water conditioners that detoxify ammonia include API AmmoLock and Kordon Amquel+. Water conditioners must clearly state they handle or deal with ammonia. Check with us before you buy.

until cycled.

The tank is cycled when ammonia reads 0.0ppm, nitrite reads 0.0ppm and nitrate increases slightly between water changes. Afterwards, you only have to add Prime during weekly water changes.


A weekly 25%-50% water change is a good habit to get into. While you’re at it, vacuum the substrate to remove solid waste, rotting food, etc. A weekly partial water change also dilutes nitrate, removes dissolved waste and replaces minerals used up by your fish and plants. Every few weeks, rinse the filter media in the water removed from the tank during the water change -- not in untreated tapwater.

Why cycle?

Fish and other aquatic animals produce ammonia as a by-product of living. Rotting food, plant debris, feces and other organics also produce ammonia. Ammonia is harmful or deadly if allowed to build-up in the tank. Cycling bacteria remove ammonia, providing the healthiest, safest water conditions for your fish. Creating a “nitrogen cycle” in the tank is how you build bacteria colonies big enough to “eat” all the ammonia.

The nitrogen cycle can take anywhere from two weeks to two months to complete.

Fish-in? Fishless?

The above instructions are for a “fish-in” cycle which uses the ammonia produced by your fish to feed the cycling bacteria and grow the bacteria colonies. Since Betta produce so little ammonia (low-bioload) smaller colonies are enough. You need just enough bacteria to eat all the ammonia. In fact, that’s what get with fish-in cycling – just the right amount of bacteria.

“Fishless” cycling means that you provide the ammonia to feed the growing colonies. You can raise very large bacteria colonies using this method. If you’re planning to stock large fish or many fish at once this may be the way to go.

Tank size

Any size tank from 2-gallons on up can be cycled using this method. The smaller 2- and 3- gallon tanks do require extra care and close monitoring; ammonia can build up pretty fast sometimes. Test daily and always be ready to do a 25%-50% water change with Prime if ammonia rises above 0.25-0.50ppm.


Two types of bacteria are involved in the “nitrogen cycle.” One kind (Nitrosomonas) oxidizes harmful ammonia and turns it into nitrite. The other (Nitrospira) oxidizes less-harmful nitrite and turns it into nitrate. After a tank is cycled the weekly water change removes nitrate.

Filter media (sponges, cartridges, pads) and substrate that contain live cycling bacteria can also be used to “seed” the cycle and make it faster. Placed in the filter or in the filter flow, these bacteria quickly grow throughout the tank. Bacteria stick to surfaces; not much lives in the water. Be careful to use only seeded media from a clean, healthy tank. Getting seeded media from a pet store can be risky.

Cycling bacteria is available in bottles from your local pet store. Tetra SafeStart is often used, although there are a few other products containing the bacteria listed above.

pH matching

Betta can tolerate a wide range of pH – from below 7.0 pH to above 8.0 pH – as long as it does not change quickly. If your tapwater pH matches your tank pH within + 0.3 points a 50% water change is no problem. If the pH difference is outside of that range, letting the refill water sit and "age" for 24-hours should bring it into range. Or you can do smaller water changes more often.

This tutorial was written by Betta Fish member Hallyx.
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