Infection in the sand?

[Tomiam]

I've cut n paste the questions from the "Read me before posting" thread to hopefully give enough information for assistance.

1~What type of fish is afflicted? In addition, please describe what is wrong with the fish to the best of your ability (i.e. cotton like growth, bloated, etc.).

Panda Corys. Ive lost two new ones in the last couple of weeks out of six. Previously to that, a month before, I lost 3 bronze corys over a period of about one month.
They dont appear to be in distress. Just that one by one they died. Upon very close examination of the panda corys I can see there is a small red patch underneath them. It looks like a rash, not oozing or mucus just red.


2~What are your tank parameters (ammonia, nitrites, nitrates, temp, pH)? Please give exact values.
Ammonia: 0
Nitrites: 0
Nitrates: 15 - 20ppm
Temp: 26 degrees.
PH: Unsure with 100% certaintity, but I believe it is 7.5

3~ How large is the tank? How long has the tank been set up?
6ft x 2ft x 2ft - Has been set up for 6 months now.

4~What type of filtration are you using? Please give the name and number (i.e. Fluval 304) and amount of gph if known.
Two Ehiem canister filters. 2217 and a 2117. Output is 1000 ltr/hr + 600 ltr/hr. Tank has a capacity of 680 ltr.


5~How many fish are in the tank? What kinds of fish are they and what are their current sizes?

13 Lemon Tetra - Adult
14 Neon Tetra - Adult
1 Golden Nugget Plec - 7cm
1 Bristlenosed Plec - 8cm
1 Clown Plec - 7cm
2 Dutch Rams - 4cm
2 Kribs - 9cm


6~When is the last time you did a water change and vacuum the gravel? How often do you do this? How much water do you remove at a time?
PWC every saturday.
Vacuum every Wed + Sat
20% PWC


7~How long have you had the fish? If the fish is new, how did you acclimate it/them?
Had the fish about a month and a half now.

8~Have you added anything new to the tank--decor, new dechlorinator, new substrate, etc.?
Nothing new.

9~What kind of food have you been feeding your fish, have you changed their diet recently?
Mixture of tetramin flake, algae wafers and catfish pellets. Once a day.



I have spoken to the LFS and they believe it is an infection in the sand substrate which is causing the corys issues. Im currently treating with Melafix. I think they are basing this partly on the fact that when I move the bogwood there is a black patch on the sand underneath it.

Any thoughts VERY welcomed.
Thank you in advance.

 

[joannde]

Do you trust the LFS ?
Also, what type of sand is your substrate ? if you roll some between your fingers does it feel nice and smooth or does it have some jagged edges ? I could imagine that if the sand is jagged that it is cutting into the cories, and those cuts are becoming infected. perhaps that is what they meant by "infection in the sand" ?

 

[Tomiam]

Yep, I definately trust them. They have won a few awards and everything Ive seen in there speaks "We care & know about what we do".

Im using silver sand, as sold by aquatic stores. Ive rolled some between my fingers and it feels pretty smooth to be honest. Its tiny grains.

Today Ive lowed the level of the sand from 30mm down to 5mm. I do admit that I was a bit shocked at the amount of sand which had turned black under the initial 5mm surface layer. When I was stirring up the tank getting the black sand out, it smelled a bit "off". Like old eggs, only not as strong.

4 hours after cleaning through, 50% PWC and getting rid of the black sand the cories are out and about rooting through the sand like Ive not seen them before! Im willing to put my hands up on his one and say "I didnt turn over the sand enough which meant rotting debris and 'bad stuff'".

I'll post if I find out anything different.

 

[Apocalypse_Gold]

Sand will get nasty if it isn't stirred. Left too long poisonous gasses build up. Some people stir it with a hanger or wire. Another option is to find something to do it for you. Some loaches like to burrow. Malaysian trumpet snails will do the same. Once you get things under control you can add more sand back in.

 

[Zagz]

The black sand is from the poisionous gases. Most likely the cause of death for your cories. As Apocalypse_Gold suggest, stirring the sand will eliminate the problem.