Kordon Methylene Blue Aquarium Review: Egg and Fungal Use
Kordon’s little blue bottle has sat on hobbyist shelves longer than most of us have kept fish, and there is a reason it keeps selling. In this Kordon methylene blue aquarium review we look at where the product genuinely earns its keep — spawning protection and fungal dips — and where newer alternatives have overtaken it. This write-up from Gensou Aquascaping at 5 Everton Park draws on years of using the 4-ounce Basic bottle in Singapore hospital tubs, breeding setups and emergency dips when a goldfish arrives from the LFS looking rough.
What Is in the Bottle
Kordon methylene blue is a 2.303 percent solution of the thiazine dye in distilled water, which works out to roughly 23 mg per millilitre. The dye is both a mild antiseptic and an electron acceptor that protects exposed fish tissue from oxidative stress. Kordon’s formula is free of zinc contamination, which used to plague cheaper medical-grade methylene blue and caused silent nitrifier die-off in hospital tanks.
Where It Actually Shines
Methylene blue’s single best use case is protecting fish eggs from saprolegnia fungus during the 24 to 72 hours between spawn and hatch. Dose 3 drops per litre in a separate hatching tub and you will see the difference immediately — unfertilised eggs still turn white and fuzzy, but fertilised eggs sail through to wiggler stage. Our methylene blue treatment guide details the ramping schedule.
Short Dips for Fungus and Open Wounds
The second real strength is the five-minute dip at 50 mg per litre in a separate container. At that concentration it penetrates the slime coat, stains any exposed fungal hyphae a vivid blue for easy identification, and oxygenates the tissue during a critical recovery window. Net the fish gently, support the body in cupped hands, and end the dip the moment gills clamp. Pair it with a supportive aquarium salt dip on alternating days for stubborn fungal patches.
Why You Should Not Dose the Display Tank
Methylene blue is indiscriminate — it binds to ammonia-oxidising bacteria just as readily as to fungal spores. Dose a display tank at therapeutic levels and you will crash the cycle within 48 hours. It also stains silicone, acrylic and light-coloured substrate permanently. Treat in a bare 40 to 60 litre hospital tub following our hospital tank setup walkthrough, and keep it away from shrimp, snails and live plants entirely.
Ich and External Parasites
Older labels suggest Kordon methylene blue for ich, but honestly the efficacy is mediocre compared to modern options. It will knock back light infections when combined with temperature and salt, but for serious outbreaks the ich treatment guide and a dedicated product like API Super Ick Cure outperform it decisively. Save the blue for what it is best at.
Dosing in Singapore Conditions
Our PUB tap water sits at GH 2 to 4 with a pH around 7, which means methylene blue dissociates cleanly and dyes the water predictably. Soft-water tanks tend to colour more intensely per drop than harder municipal supplies, so err on the lower end of label dosing — 2 drops per litre for egg protection rather than the stated 3. Tropical ambient at 28 to 30 degrees also accelerates oxidation of the dye, so top up every 24 hours in breeding tubs rather than trusting a single dose to last three days.
Availability and Pricing Locally
The 4-ounce Basic bottle runs $14 to $18 at Iwarna Aquafarm, C328 Clementi and most Thomson Road shops. The 16-ounce Professional size at around $38 is better value if you breed regularly or keep a rotating hospital tank. Shopee listings from authorised Kordon sellers occasionally dip to $12 with free shipping, but watch expiry dates — the dye oxidises slowly in the bottle and loses potency after three years.
Safety and Staining Reality
Methylene blue stains everything. Wear gloves, work over a sink, and expect blue fingernails for a day if you slip. On SP Group tiled HDB kitchen floors a spill wipes off reasonably well within ten minutes; on unsealed grout it is permanent. Clothing staining is immediate and total. Keep the bottle out of reach of children — it is not acutely toxic, but a swallowed mouthful will trigger vomiting and alarming blue urine for a week.
Comparison With Alternatives
API Fungus Cure uses victoria green and acriflavine instead, which is arguably stronger on established fungal patches but more toxic to scaleless fish and plants. Seachem ParaGuard is a modern malachite-green-free alternative that handles ich and fungus together without crashing filtration as hard. For eggs specifically, nothing has displaced methylene blue — that is still its niche.
Who Should Keep a Bottle
If you breed anything that lays eggs, you need methylene blue on the shelf. If you keep a hospital tank for occasional sick fish, the dip protocol justifies a small bottle alongside your aquarium salt and praziquantel. Casual community keepers with no breeding plans can skip it in favour of broader-spectrum tools. Stored in a cool cupboard away from direct sunlight, a bottle will last three to four years before fading.
Verdict
Kordon methylene blue remains the benchmark for egg protection and short fungal dips. It is not a general-purpose fish medication, and anyone pitching it as a one-bottle-cures-all has not used it properly. Buy it for breeding and emergency dips, respect its filtration-crashing potential, and it will sit quietly on your shelf earning its place for years.
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emilynakatani
Still Have Questions About Your Tank?
Drop by Gensou Aquascaping — most walk-in questions get answered in under 10 minutes by someone who has set up hundreds of tanks.
5 Everton Park #01-34B, Singapore 080005 · Open daily 11am – 8pm
