Glutaraldehyde, widely known in aquaristics under the trade names “Seidex” (Sajdex) or “Seachem Flourish Excel,” is one of the most powerful and discussed tools in the experienced aquarist’s arsenal. This chemical component performs two key functions: it serves as a source of organic carbon for aquatic plants and acts as a highly effective algaecide, capable of eliminating even the most stubborn types of algae. The use of glutaraldehyde requires precise adherence to dosages and an understanding of its chemical action to avoid harm to sensitive aquarium inhabitants.
What is Glutaraldehyde (Seidex) and How Does it Work Against Algae?
Glutaraldehyde (GA) is an organic compound from the dialdehyde group. In aquaristics, a 2.5% solution is typically used, which is strong enough to combat lower algae but relatively safe for higher plants and most fish when dosed correctly.
Chemical Mechanism of Action
- Carbon Source: Upon entering the water, GA decomposes, releasing components that aquatic plants can use for photosynthesis. This is especially important in aquariums without CO₂ supply, where it acts as a substitute or supplement to carbonic acid.
- Algaecidal Action: The primary function for which it is used is algae elimination. Glutaraldehyde is a potent biocide. It actively interacts with proteins and amino acids in algae cells. The aldehyde groups disrupt the structure of cell membranes and enzyme systems, causing rapid algae death.
Important to understand: Higher aquarium plants (e.g., Cryptocoryne or Anubias) can tolerate dosages that are lethal to algae due to their more complex cellular structure and detoxification mechanisms. However, with significant overdose, they can also suffer.
Types of Algae Most Sensitive to Seidex
Seidex shows excellent results in combating the following types of algae:
- Black Beard Algae (Compsopogon spp.): One of the most persistent algae, which quickly dies off with shock doses.
- Audouinella spp. (similar to Black Beard): Similar to black beard, also responds well to treatment.
- Xenococcus: Green spot algae, which often cover glass and slow-growing leaves.
- Filamentous Algae (Spirogyra or Oedogonium): Long, thin green threads, particularly sensitive to spot application.
Seidex Application Instructions: A Step-by-Step Guide for Aquarists
The application of glutaraldehyde is divided into two main methods: daily dosing (as a carbon source and for prevention) and shock treatment (for eliminating algae blooms).
1. Preparation and Dosage Calculation
Always use a 2.5% solution. Dosage calculation is based on the net water volume in the aquarium (total volume minus substrate, decorations, and equipment).
Dosage Table (for 100 liters of net water volume):
- Preventive (Carbon) Dose: 1–1.5 ml daily. Used to stimulate plant growth and suppress minor algae.
- Working/Therapeutic Dose: 2–3 ml daily. Used for moderate algae blooms. Course: 10–14 days.
- Shock Dose (Algaecidal): 4–5 ml once. Used for rapid elimination of black beard and filamentous algae.
2. Application Methods
A. Daily Dosing (for Plants and Prevention):
- Apply the calculated dose once a day, preferably in the morning, 1 hour before or immediately after turning on the lights.
- Dilute the required amount of Seidex in a small volume of aquarium water (50–100 ml).
- Slowly pour the solution into an area of strong current (near the filter outlet) to ensure rapid distribution throughout the entire volume.
B. Shock Treatment (Algae Elimination):
Shock treatment requires increased attention, as high concentrations can cause oxygen starvation in fish and shrimp.
- Before Dosing: Increase aeration (turn on the air pump or raise the filter outlet).
- Procedure: Apply 4–5 ml per 100 liters once. If algae cover a large area, the procedure can be repeated after 2–3 days, but no more than 3 times in a row.
- Observation: During the first 4–6 hours, carefully monitor fish behavior. If they are breathing heavily or surfacing, perform an immediate partial water change (20–30%).
C. Spot Treatment:
This method is ideal for combating localized outbreaks, such as black beard on driftwood or Anubias barteri leaves.
- Turn off the filter and aeration to stop water flow.
- Draw Seidex into a syringe (without a needle).
- Slowly apply 5–10 ml of the solution, directing the stream directly onto the algae-affected areas.
- Wait 15–20 minutes to allow the solution to act, then turn on the filter and water flow.
- Result: Within 1–3 days, the treated algae should change color from black/green to red or white, indicating their death.
Precautions When Working with Seidex: Safety First!
Glutaraldehyde is a strong chemical that can be hazardous to human and animal health in concentrated form.
1. Handling Precautions
- Ventilation: Work with the product in a well-ventilated area. GA vapors can irritate mucous membranes, eyes, and respiratory tract.
- Gloves: Always use nitrile or latex gloves. Prolonged skin contact can cause irritation and dermatitis.
- Eye Protection: Protective eyewear is recommended, especially when handling large volumes or concentrated solutions (e.g., 25% medical grade).
- Storage: Store the product in its original, tightly sealed container, out of reach of children and pets. Avoid direct sunlight.
2. Emergency Procedures
Skin Contact: Immediately wash the affected area with plenty of running water. Remove contaminated clothing.
Eye Contact: Rinse eyes with water for at least 15 minutes, keeping eyelids open. Seek immediate medical attention.
Ingestion: Do not induce vomiting. Drink a large amount of water or milk. Seek immediate medical help.
Seidex Compatibility with Aquarium Inhabitants: Who Might Be at Risk?
While glutaraldehyde is relatively safe for most healthy fish, it can pose a threat to some sensitive organisms, especially when using shock doses.
1. Sensitive Invertebrates
Seidex poses the greatest danger to crustaceans and mollusks. Their respiratory systems and cellular structures are particularly vulnerable to aldehydes:
- Shrimp: All types of shrimp, especially dwarf shrimp (e.g., Cherry, Amano, Crystal), are extremely sensitive. Even working doses can cause their death. Recommendation: During shock treatment, it is recommended to temporarily remove shrimp.
- Snails: Apple snails, Nerites, Ramshorns, and Malaysian Trumpet Snails may show signs of poisoning (close up, become lethargic) or die at high concentrations.
2. Sensitive Fish
Special caution should be exercised when keeping fish that are sensitive to water quality and low oxygen levels:
- Loricariidae Catfish: Some species, especially Otocinclus affinis (Otos) and young Ancistrus, may react poorly to GA.
- Air-Breathing Fish: Labyrinth fish (bettas, gouramis) and Corydoras (Corydoras spp.) may be more susceptible to stress from changes in water chemistry.
General Rule: If sensitive species are present in the aquarium, never exceed the therapeutic dose (3 ml per 100 L) and always ensure maximum aeration.
3. Impact on Plants
Most popular aquarium plants (Echinodorus, Vallisneria, Hygrophila) tolerate Seidex well and even use it as a carbon source. However, some delicate or liverwort mosses may be sensitive to shock doses:
- Mosses: Mosses of the genus Taxiphyllum (Java Moss) and Riccardia chamedryfolia may temporarily slow growth or suffer chemical burns.
- Vallisneria (Vallisneria): Excessive doses can cause leaf “melting.”
After Using Seidex: Aquarium Maintenance and Preventing Recurrence of Algae
Eliminating algae is only half the battle. To prevent their recurrence, it is necessary to stabilize the aquarium ecosystem and address the root cause of the bloom.
1. Actions Immediately After Treatment
- Removal of Dead Organic Matter: After shock treatment, dead algae will begin to decompose. This can lead to a spike in nitrates and phosphates. Thorough substrate siphoning and removal of large clumps of dead beard algae are necessary.
- Water Change: 24–48 hours after a shock dose, a 30–50% water change is recommended to remove excess chemicals and algae decomposition products.
- Filter Cleaning: Check filter media. Dead algae can clog sponges, reducing filtration efficiency.
2. Long-Term Stabilization
Algae appear when the balance between light, CO₂ (carbon), and nutrients (NPK and micronutrients) is disrupted. Success in aquaristics is about parameter control, not just chemical warfare.
- Light Optimization: Ensure that light intensity and duration (usually 8–10 hours) are appropriate for your plants’ needs. Too much or too bright light is a common cause of blooms.
- Nitrate and Phosphate Control: Regularly test water. Maintain the ratio of nitrates (NO₃) and phosphates (PO₄) within recommended limits (e.g., 10:1 or 15:1).
- Regular Maintenance: Weekly water changes (25–30%) are essential to remove excess organic matter and maintain stable water chemistry.
FAQ: Answers to the Most Popular Questions About Using Seidex
Q. Is it true that glutaraldehyde is “liquid CO₂”?
A. No, this is a marketing simplification. Glutaraldehyde is not CO₂. It acts as a source of organic carbon that plants can utilize when CO₂ is limited. It’s a useful substitute, but not an element identical in action.
Q. How long can Seidex be used?
A. If you are using it as a carbon source (preventive dose), it can be applied daily indefinitely. If you are performing shock therapy, the course should not exceed 10–14 consecutive days. After eliminating algae, it’s best to switch to a preventive dose or stop dosing altogether if the aquarium has sufficient CO₂.
Q. What to do in case of accidental overdose?
A. Immediately perform the largest possible water change (50–70%). Increase aeration and turn on an additional air pump. Carefully monitor fish and shrimp. Glutaraldehyde decomposes quickly, but high concentrations can cause chemical burns to the gills.
Q. Does Seidex affect nitrifying bacteria in the filter?
A. When using recommended dosages (even shock doses), glutaraldehyde does not have a significant negative impact on nitrifying bacteria colonies (Nitrosomonas and Nitrobacter) living in the filter. They are much more resistant to GA than algae.
Q. Can the medical 25% solution be used?
A. Yes, but with extreme caution. Medical “Cidex” often has a concentration of 25%. It must be diluted 10 times to obtain a working 2.5% solution. Calculations must be extremely precise, as an error in calculating the 25% solution is lethal to all aquarium inhabitants.
Interesting Facts About Glutaraldehyde and Algae Control
The history of glutaraldehyde in aquaristics is closely linked to its industrial applications.
- Medical Standard: Before becoming a popular algaecide, glutaraldehyde was used in medicine and dentistry as a highly effective disinfectant for equipment. It is capable of destroying spores, viruses, and bacteria.
- Biodegradation: Glutaraldehyde is a biodegradable compound. In an aquarium, it decomposes rapidly, especially under light and with aeration, transforming into less toxic organic acids and carbon compounds that can be utilized by plants.
- pH Influence: The effectiveness of glutaraldehyde as a biocide is higher at lower pH values (acidic environment). In alkaline water (high pH), it loses its activity faster.
- Algae “Melting”: A characteristic sign of successful Seidex treatment is that algae (especially beard algae) turn pink, red, or white. This occurs due to the destruction of chlorophyll and cellular structures. Afterward, they are easily removed by cleaner fish (e.g., Crossocheilus siamensis) or mechanically.
The use of glutaraldehyde is a powerful, but responsibility-requiring method. By applying it according to instructions and observing safety measures, the aquarist gains an effective tool for creating a clean and healthy planted aquarium.