I'm in need of a critique

[H Taylor]

I'm in need of a critique. On January 2nd I did my normal 50% WC in both aquariums. Then on January 8th cleaned the canister filter on my 29g tank. Next day everything's fine. On the 10th at feeding time all's well but just before lights out, 4 blackskirt tetra were on the surface, swimming maniacaly but not gasping, their gill covers weren't moving. The water had taken on a slightly smokey appearance. I took a sample of water and did a 75% WC then tested the sample taken before WC.
The results were:
PH 6.6
ammonia 0.00 ppm
Nitrite 0.00 ppm
Nitrate 20 ppm
Phosphate 10 ppm
GH 53.8 ppm
KH 35.7 ppm
temp 76.5 F

No new additions to the livestock or plants in the last two months.
Fish:
5 albino cories , 5 peppered cories ,
2 emerald cories, 2 BN Plecos, 6 blackskirt tetras , two TB nerita , 1 assassin snail, 1 male platy,
Plants:
Java ferns , dwarf saggatera , dwarf chain swords , Amazon sword , mysis, cabomba
Hardscape:
Red strata rock , mopani log, Caribsea peace river gravel.

Aquarium has been established for 3 years, with no problems, with the exception of a heater malfunction that killed 6 older fish. After the WC, all fish were a little skittish but otherwise normal. The next morning I found 3 blackskirt tetra, the biggest peppered Cory, both emerald cories, 1 albino Cory dead. The rest of the livestock, except for 2 blackskirts ,were unable to swim normally. They couldn't balance resting and when they tried to swim, they corkscrewed wildly for 2 or 3 seconds then freeze-up, falling uncontrolled,stiff for up to a minute. Then unable to right themselves, they just flopped slowly then takeoff again 5 to 10 minutes later. 2 juvenile blackskirt tetra appeared to not be affected at all.
I did a 95%+ WC, leaving just enough water so the fish could get oxygen and refilled the tank. Then I put a hob filter on it, with 2 charcoal bags, and added 2 air stones. Then I cleaned the canister filter using dechlorinated tap water. I replaced all the filter media and added the remainder of my charcoal. I rinsed the bio-media very well, removing all detritus with temp correct dechlorinated tap water.
The tank still had a slight cloudiness and the fish weren't improving so I did another 90% WC and started the canister filter. I removed two cories because they had been physically injured and placed them in a emergency hospital container of 1.5 gal., added salt at the rate of 2 tbls./5 gal. I also added salt to the whole tank at the rate of 1 tbls./5 gal. The next morning, 1 dead fish in the hospital tank but the rest were alive with little improvement.
Did another 90% WC, I waited till late after noon, did another 90% WC. I repeated 2 WC per day till Saturday when I did just 1 90% WC along with making preparations to rehouse the survivors in a big plastic tote.
Today I got the remainder of the fish into their temporary home. Another Cory had been attacked overnight and was missing his caudal fin w/massive bruising. As much as I hate to euthanize a fish, I went ahead and ended his suffering. The others seem to be regaining their control but still not interested in food.
Is there anything else I should do to help the situation? Is there anything I should have done and didn't? Or did and shouldn't have done? Now that I have torn down the tank, should I attempt to clean the decor and tank or just replace the whole thing? I'm going to replace the substrate and plants regardless. No one but myself has been in the house since the week of CHRISTmas. I know a contaminant of some type must have gotten into the tank, so I'm the guilty party.
My 10g is doing great, even with the snails. I use the same dechlorinator, same fertilizer, same gravel vacuum and same refill system on both tanks. I do use seperate nets and hand tools, mainly due to the size difference, 10 gal vs. 29 gal.
Any suggestions, corrections or tongue lashings will be accepted, but remember its been a very long week for me.
H Taylor

 

[NannaLou]

I’ve no idea what might be going on, someone with more knowledge will surely give some opinions soon.

Sorry you are having such a tough time at the moment. You don’t sound like a lazy fish keeper, it sounds like a random act so don’t be too tough on yourself.

 

[GaryE]

Maybe this could connect, if you are on municipal water. I don't know how Mississippi works, although it was a standard in spelling bees when I was a kid so it was fun to type.
It's standard here for the municipality to flush the water mains chemically twice a year, overnight, to break up scale on the walls of the pipes. Only once have I done a water change in the morning after it was being done, and what happened sounds a lot like what you describe. Grey cloudy water and fish deaths, mainly of adult fish. Juveniles survived it.

 

[Byron]

Something toxic has got in the water in the aquarium, and assuming the tests are accurate it is not ammonia/nitrite related. Nitrate at 20 ppm is high, but not so high it is the cause of such sudden demise in the fish. Phosphate at 10 ppm is very high, but so far as I know this would not kill the fish like this [I stand to be corrected, phosphate poisoning is new to me].

@GaryE has one good idea; check with your water authority to see if they have done this recently, flushing the system, using chemicals, etc. Another similar thought is household chemicals like solvents, cleaners, perfumes, anything possibly spilled in the tank?

Symptoms are identical to what I had with a toxic fungus from a chunk of wood. I cannot see the mopani wood in the photos in post #1...is there any sign of a whitish fungus/mold/slime on any part of the wood? How long have you had the wood?

The fish are in another tank now, keep them there, and do not put anything in that tank that comes from the problem tank. A point for the future, your water is very soft and unsuited to livebearers, so don't acquire any more of those (platies, etc). This was obviously not the issue here, but I did notice the GH and pH and the numbers are ideal for soft water species but not hard water fish.

 

[H Taylor]

Thanks for the responses all.
GaryE I will check with the Water Dept. tomorrow and see if they have added anything new to the water or been doing any maintenance to the system. Thanks for the idea.
NannaLou I've been in rougher situations in my life I'm sure, but this one ranks near the top, thanks.
Byron my tap water is 5 ppm nitrate and the phosphate varies, usually around .5 ppm . I recently changed brands of their food in an attempt to improve their diet and lower the excess phosphate input.
The platy in the picture is the last of a group of 4 that were dropped on my doorstep by a neighbor whose kid "lost interest". I try to keep to fish from S.America. The soft water, low PH, blackwater type fish. The platy had injuries (5 red dots surrounded by light gold halos) below the lateral line, behind the vent, that I didn't notice until I looked at the photos, he is one of the survivors.
The log came from chewy last fall. When I was removing the water and decor there was a grayish-white slime underneath the log and rock, on the gravel that wasn't compressed under them. It had an awful smell that I thought was a nerita . I found the snail later when I took the return line out. It was when I was netting the fish that I noticed the slime, but I stirred it up before I thought to take a photo.
I'm very careful with all chemicals in the home. I have allergies to many common household and grooming products.
Many thanks for helping to stir my grey matter, what little I have left. I most definitely will not be using anything from the affected tank in the temporary tank. I did have to use the bare heater, w/o it's brackets. I soaked it and scrubbed it in saltwater 6 times, wiped it once with white vinegar and then rinsed it in tap water. I had to set up the hospital tank and I used my spare heater for that.
I guess since nothing sticks out as being the culprit, I'll be shopping for a new aquarium or two. Sorry for the time it took to reply, but with the last week's snafu and my mobility troubles it just takes more time now days.