Maintaining proper water parameters is crucial for a healthy aquarium. One important parameter is carbonate hardness, which measures the amount of carbonates and bicarbonates dissolved in the water. A high carbonate level can cause issues like stunted growth and difficulty molting for shrimp and other invertebrates. Luckily, there are several methods aquarists can use to lower carbonate hardness in a fish tank. This article will discuss why high carbonates are problematic, how to test and monitor carbonate levels, and effective ways to reduce carbonate concentration for a thriving aquarium.
Why Is High Carbonate Harmful in a Fish Tank?
Carbonates and bicarbonates are naturally present in tap water at varying concentrations depending on the water source. In moderation, these compounds help buffer pH changes in the aquarium. However, at high levels carbonates can negatively impact livestock health.
Effects on Aquatic Life
- For shrimp, high carbonate hardness interferes with the molting process and causes stunted growth and failed molts. This affects delicate species like cherry shrimp and crystal shrimp that need soft, acidic water.
- Snails like nerites also struggle with high carbonates, which can erode and weaken their shells over time.
- Fish are less directly impacted, but excessive carbonates reduce oxygenation which stresses respiration. Some species also exhibit poorer growth and coloration.
- High carbonates encourage algal growth, potentially leading to blooms and imbalanced aquarium chemistry.
Water Chemistry Changes
Carbonates directly influence water parameters like pH and KH:
- They increase pH, making the water more alkaline. Values above the ideal range stress fish sensitive to basic water.
- Carbonates are the main contributor to high KH values. KH measures the total buffering capacity, which is elevated with more carbonates present.
- Rapid pH fluctuations also occur as carbonates interact with other chemicals like CO2. These swings stress livestock.
Tips for Testing Carbonate Levels
Since elevated carbonates can negatively impact aquatic life, routine testing is recommended. Here are some tips:
- Use a KH test kit to measure carbonate concentration. KH and carbonates have a direct relationship, so testing KH provides an accurate carbonate reading.
- Test KH both straight from the tap and inside the aquarium. This checks both water source KH and the effect of additives.
- For aquariums with shrimp and snails, KH levels above 5 dKH indicate carbonates should be reduced. Aim for 2-4 dKH.
- Test 1-2 times per month to stay on top of any fluctuations, especially if experiencing livestock health issues.
- Consider sending a tap water sample to a lab annually to test for TDS, GH, KH, pH, and other parameters.
Methods to Lower Carbonate Hardness
If testing reveals carbonate levels are too high, action should be taken to create a more favorable environment for fish, shrimp, and snails. Here are effective methods to reduce carbonates in an aquarium:
Use Carbonate-Free Replacements for Tap Water
One of the easiest ways to control carbonates is using an alternate water source for water changes and top-offs. Some options include:
- Distilled or reverse osmosis (RO) water – These have minimal TDS and KH, providing a carbonate-free water replacement. They can be mixed with tap water to achieve the desired hardness.
- Rainwater or meltwater – Naturally soft sources like collected rain or melted snow also have lower carbonates than tap. They offer a free alternative to distilled/RO water.
-Filtered water – Tap water run through a sediment filter or KH-removing media decreases carbonates. Phosphate-removing media also helps.
Perform Small, Frequent Water Changes
Carbonates accumulate naturally in an aquarium over time. Performing small but more frequent water changes helps flush them out before levels get too high.
- Change 10-15% of the water 1-2 times per week rather than 30%+ monthly.
- Use a gravel vacuum to remove debris that may be leeching carbonates.
- Always replace with carbonate-free water like distilled or RO.
Add Products That Bind Carbonates
Specialized products are available that bind and remove carbonates from the water column. They can be added daily or as-needed to lower KH/carbonate levels.
- Seachem Acid Buffer – Neutralizes carbonates and lowers pH. Dose 1 tablespoon per 20 gallons to reduce KH by 1 dKH.
- Seachem Alkaline Buffer – Works similarly but is phosphate-free.
- Fluval Peat Granules – Release tannins that softly acidify water and reduce carbonate concentration.
- Driftwood – Leaches tannins like peat for a natural carbonate-reducing effect.
Use Carbonate-Removing Filter Media
Filter media designed to strip KH from the water will also remove carbonates. This provides continuous reduction between water changes.
- Polyfilter floss has ion-exchange properties that adsorb carbonates. Needs replacing monthly.
- Phosphate-removing media like PhosGuard will also reduce KH and associated carbonates.
- Commercial deionization or softening resin media removes carbonates and other minerals.
Culture Tannin-Releasing Plants
Certain plants can be grown in an aquarium to release tannins that gently lower pH and carbonate hardness. Good options include:
- Indian almond leaves
- Catappa leaves
- Oak leaves
- Alder cones
- Peat moss
Simply add leaves/cones directly to the tank or water. No special setup required!
Use an RO/DI Water Filtration Unit
For aquarists looking to remove carbonates from tap water before it enters the tank, a reverse osmosis/deionization (RO/DI) unit is the most thorough option.
- RO filtration first removes nearly all TDS, carbonates, minerals.
- DI polishing then removes remaining trace elements missed by RO.
This process produces pure, mineral-free water – essentially a blank slate that can be remineralized as needed.
While more expensive upfront, an RO/DI unit provides a convenient source of carbonate-free water for aquarium use.
What Level of Carbonates Is Ideal in an Aquarium?
The ideal carbonate level depends on the livestock kept:
- For sensitive shrimp and snails, target 2-4 dKH and soft, acidic conditions. Stay under 5 dKH.
- Fishes prefer slightly harder water from 5-10 dKH. Rift lake cichlids need 10-15 dKH.
- Aim for lower end of a species’ range and make adjustments from there based on health and breeding success.
Can You Raise Carbonates If They Get Too Low?
If carbonate hardness drops too low, livestock health can also suffer. Some ways to safely raise KH and associated carbonates include:
- Perform smaller, less frequent water changes to allow buildup.
- Add alkaline buffering products like Seachem Alkaline Buffer, sodium bicarbonate or calcium carbonate. Start with small doses.
- Mix in some tap water, which contains natural carbonates, when replacing water.
- For planted tanks, stop using carbonate-removing products and let levels stabilize through natural processes.
Monitoring carbonate concentration and maintaining an appropriate range for the livestock is key. Never let KH or pH crash severely. Stability is best!
FAQ
How do carbonates affect pH?
Carbonates directly influence pH by increasing alkalinity. pH is a measure of alkalinity vs acidity. The more carbonates present, the more alkaline or basic the water becomes, and pH rises. Removing carbonates has an acidifying effect that lowers pH.
What is the relationship between KH and carbonates?
Carbonate hardness is a measure of dissolved carbonate and bicarbonate ions. KH tests measure alkalinity, which is caused almost entirely by these carbonate compounds. So KH has a direct relationship with carbonates – as carbonates increase, KH rises predictably. KH can therefore be used to estimate carbonate concentration.
Can low carbonates harm fish?
Extremely low carbonate levels are also detrimental. With inadequate buffering, pH can crash leading to acute toxicity. Rapid pH fluctuations also occur when KH is too low. For most community fish, aim for moderate carbonate hardness around 5-10 dKH for a stable, buffered system. Sensitive species like tetras and rasboras prefer KH in the lower part of this range.
What household items can remove carbonates?
Some common household items that can bind and remove carbonates include:
- Peat granules or peat moss media – The tannins released lower pH and soften the water.
- Driftwood – Also releases tannins for a natural carbonate-reducing effect.
- Natural leaves – Dry leaves from oak, alder, catappa, and Indian almond trees release carbonate-lowering tannins.
- Wood vinegar – The acidic vinegar leaches from decaying wood and reduces KH/carbonates.
- Sphagnum moss – This versatile moss naturally softens water chemistry.
- Food grade citric acid – Can be dosed in small quantities to lower carbonate hardness and pH.
Is carbonate hardness the same as KH?
Carbonate hardness and KH measure the same thing – the concentration of dissolved carbonates and bicarbonates in the water. They are essentially two terms for the same water parameter. KH is the more modern, accurate name as it describes the alkalinity conferred by carbonates rather than just general “hardness”.
How can I lower KH in my tank?
Some effective ways to lower high KH caused by excess carbonates include:
- Use distilled, reverse osmosis, or deionized water for water changes. These have negligible KH.
- Add tannin-releasing botanicals like driftwood, leaves, cones. Tannins gently lower KH.
- Dose a KH-lowering product like Seachem Acid Buffer or Fluval Peat Granules.
- Run water through peat filters or ion exchange media to strip KH.
- Perform more frequent, smaller water changes to dilute KH buildup.
- Stop using alkaline buffers and let KH decrease over time through natural processes.
Conclusion
Maintaining an appropriate carbonate level is important for a healthy aquarium environment. By understanding the impacts of high carbonates, routinely testing KH, and utilizing various removal methods, aquarists can achieve the ideal carbonate range for their livestock. This prevents issues like failed molts, shell erosion, stress, and pH swings. Investing some time into monitoring and adjusting carbonate hardness helps every inhabitant of the aquarium thrive.