Potential Velvet Problem - seek diagnosis & cure reccos

[Dave B.]

Thanks for reading. Requested information below. Looking to see if my amateur diagnosis seems correct and how I should treat the fish and display tank. I have a 30 Gal tank and Fluval 306 filter I could set up as a QT, but still would need to treat the planted 75 Gal display tank.

Tank size: 75 Gal with Fluval FX4 filter (upgraded from an established 55 Gal a month ago)
pH: 7.6 (Hard to be exact since it is between the standard high/low PH test scales)
ammonia: 0
nitrite: 0
nitrate: 5
kH: unknown
gH: unknown
tank temp: Initially 76 F, raised to 83.5 F based on reading online treatments

Fish Symptoms: Longfin Zebra Danio died off. Fins turned partly yellow, some flashing. Stayed at the top of the tank toward the end - possibly gulping air, but I didn't notice. Concerned that the tank has Oödinium infestation.

Volume and Frequency of water changes: 15 Gal every other week

Chemical Additives or Media in your tank: Just API Stress Coat at this point. Am considering Chloramine Phosphate or Coppersafe

Tank inhabitants: 1 Black Neon Tetra, 1 (remaining) Longfin Danio, 1 Golden Zebra Danio, 3 Bandit Cory, 2 Albino Cory, 6 Harlequin Rasbora, 1 Bristlenose Pleco, 4 Dwarf Gourami, 6 Black Skirt Tetra, 6 Glolight Tetra, 6 Bloodfin Tetra, 1 Farlowella Cat, a few Assassin Snails, several Sword-type plants

Recent additions to your tank (living or decoration): Glolight Tetra, Bloodfin Tetra, & Farlowella Cat are recent additions, but we had a slow, progressive die-off in the previous 55 Gal tank that held many of the other fish prior to these fish arriving. That could have been the same problem or a different problem.

Exposure to chemicals: none known

Digital photo (include if possible): These are of the deceased fish. The white spots are light reflections, not actual spots on the fish.

 

[Colin_T]

It's not Oodinium.
To check for Oodinium, wait until the tank lights are off then shine a torch on the fish. See if any of them have a yellow/ gold sheen to their body. If they do, and the fish are rubbing on objects, then it's Oodinium.
*NB* They can have other issues (protozoan or bacterial infections) in conjunction with Oodinium.

I'm not sure about the yellow fins, that could be natural colouration.

The fish does appear to have a bacterial infection (red around the belly, and creamy white patch on rear half of body).

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Post more pictures and video of the remaining fish.

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Wipe the inside of the glass down with a clean fish sponge.

Do a 80-90% water change and gravel clean the substrate every day for a week or until we work out what is going on.
Make sure any new water is free of chlorine/ chloramine before it's added to the tank.

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Add some salt.
You can add rock salt (often sold as aquarium salt), sea salt or swimming pool salt to the aquarium at the dose rate of 2 heaped tablespoon per 20 litres of water.

If you only have livebearers (guppies, platies, swordtails, mollies), goldfish or rainbowfish in the tank you can double that dose rate, so you would add 4 heaped tablespoons per 20 litres (5 gallons).

Keep the salt level like this for at least 2 weeks but no longer than 4 weeks otherwise kidney damage can occur. Kidney damage is more likely to occur in fish from soft water (tetras, Corydoras, angelfish, gouramis, loaches) that are exposed to high levels of salt for an extended period of time, and is not an issue with livebearers, rainbowfish or other salt tolerant species.

The salt will not affect the beneficial filter bacteria but the higher dose rate will affect some plants. The lower dose rate will not affect plants.

After you use salt and the fish have recovered, you do a 10% water change each day for a week using only fresh water that has been dechlorinated. Then do a 20% water change each day for a week. Then you can do bigger water changes after that. This dilutes the salt out of the tank slowly so it doesn't harm the fish.

If you do water changes while using salt, you need to treat the new water with salt before adding it to the tank. This will keep the salt level stable in the tank and minimise stress on the fish.

 

[Dave B.]

Thanks for the response. Will start the water change process.
Based on what you said my tetras and gouramis (most of the tank) aren't salt tolerant. Is the 2 tsp/20 L dose safe for them and my plants? What is the range between the minimum effective dose and the max safe dose for those fish?
New pictures of the tank added. I just noticed the spot that looks like a sore on the golden zebra danio. I have video, but even 10 sec is being rejected as too large to post.