my Nose Dying

Question
Hi Karen,

I am a repeat customer here. You have been great answering to my previous queries; that's why I want to field you some questions again.  Lol.  

Recently, I vacuumed the sand in my 3-ft planted tank and did a change of water afterwhich the water turned cloudy.  I poured in some liquid solution bought from the fish shop to    dissolve the cloudiness and although it worked, the result was disastrous as all my fish started dying and by the end of the day, all my fishes (neon tetras, black neon tetra, rummy nose, zebra, white cloud mountain) were wiped out.  Although I followed the instruction on the liquid solution strictly when applying it, I believe it could be the cause of the death.

The next day, I did several change of water before I added new fishes (similar species except rummy nose) into the tank and they have been fine till date.   Last night, I bought 15 rummy nose and I woke up this morning to find them all dead.  The other fishes are doing fine.

Recently I bought a simple CO2 cannister from the fish shop just to provide CO2 for the plants.   In fact, after using the CO2, I noticed the plants are growing faster and the fishes look better.

What could be the cause of the death of the rummy nose and how can I prevent a recurrence when I re-stock them in my tank?  

Answer
Dear Lawrenz,
This is a difficult one. It would be great to know what levels your ammonia,nitrite and nitrate are and your pH level as well.

It could be possible that the CO2 Canister you recently added to your aquarium may have caused too much co2 in your aquarium, especially during the nighttime when plants release carbon dioxide themselves.  Sometimes CO2 can cause pH levels to flucuate, and it could be possible that your tap or source water may have had a different pH than what your aquarium was currently at. As you know, pH flucuations can often cause fish loss.

I'm not too sure about the liquid product for the cloudinesS. I never like to use too many chemicals in my aquariums but there is a chance the liquid product caused some reaction to the fish.

Something severe has gone on for all your poor tetras and  Mountain minnows to have such a major die-off. Have you done a thorough investigation of the water quality when this happened? Did the water have any odd smell to it, how about the ammonia, nitrite, nitrate and pH levels? Was there a temperature flucuation during the water change? Could the source or tap water have been different in chemistry than your aquarium's? Were you sure to use dechlorinator and plenty of it during the water change? Is it possible that areas of your sand bed became impacted and anerobic (clogged with debri and creating an no-oxygen environment) and when you stirred up debri it was overwhelming to the fish? I have had experiences in the past with planted aquariums that had too many pockets of impacted gravel clogged with debri, my fish were gasping and fish loss was high. I found out that nitrites and ammonia was high. When I transferred all the survivors as quickly as possible to another aquarium, they improved within 5-10 minutes--no more gasping at the surface and behaving listless. They began schooling and behaving naturally. Since doing a major gravel vacumming and large daily water changes, the nitrites were controlled and disapeared back to a normal ZERO reading.
I believe the impacted gravel and excess debri that is so frequent in a planted aquarium possible overwhelmed the bacterial colonies and the result was a ammonia and nitrite spike. This could be compared to somebody overfeeding their aquarium.

This problem is even more acclerated with a sand bed since sand impacts very quickly. The solution to this is ideally removing the fish to a healthier environment in a different aquarium and doing a severe gravel/sand vacumming and stirring up any clogged areas. Water changes and vacummings will have to be repeated every day until everything is healthy once again.

I really hope this helps give you some ideas about your aquarium's trouble. If you have anymore questions or concerns, feel free to write!

Best wishes and Happy holidays!
Karen~