Rapid die-off, quite inexplicable. Help?

[MacDracor]

1~Started with a gold gourami sitting on the bottom. Then I noticed my crawdad eatiog my male lyretail molly. The gourami seems to be ok now, but over the course of about 12 hours, the two remaining (silver) mollies, all 7 guppies, and one swordtail have died. They just stop swimming and either drift around the tank, float, or sink. No white spots, no visible parasites, no swelling or redness of the gills, though a couple of fully dead ones seemed to have their head cocked to the side slightly. Now the rest of the swordtails are looking listless, and the gouramis have started holding their fins tight against their bodies.

2~Tank Parameters: Nitrate - 10 ppm, Nitrate - 0 ppm, Hardness - 75, Chlorine - 0, Alkalinity - 80, pH - 6.8

3~ 29 gallon tank, set up for about 4 months, substrate and plants transferred from a 20 gallon that had been set up for about 6 months.

4~TopFin 20, rated for up to 30 gallon tanks, not sure of GPH

5~Fish in tank (* indicates dead and removed)Two adult and 1 fry mollies*, 7 guppies*, 4 swordtails, recently of breeding age, 3 gourami (1 each Gold, Opaline, Pearl), about 2 inches each, 2 crawdads. I know this is a heavy bioload, but it's heavily planted and I change the filter regularly. Never had a problem like this.

6~Water change maybe 4 days ago, did a 20% change when I saw the first dead fish. Generally do 5 gallon changes every week or so.

7~The gouramis are the newest, having been in the tank only about a month. All others either bred or 6+ months.

8~Nothing new added in over a month.

9~Morning feeding is a mix of tropical Omega One fish flakes, algae flakes, freeze dried bloodworms, and sinking algae wafers for the crawdads. Evening feeding is alternating frozen (but thawed before feeding) brine shrimp or mysis shrimp.

Most likely unrelated note, today has been an emotional horror for me, and I felt like crying even before I noticed all my fish dying. Please help...

 

[Mr. Limpet]

What's you're ammo level, or is that what you're referring to as Chlorine? Sounds like you're tank is in good shape, but aren't crawdads pretty aggressive? He could be going after them and compromising their QOL.

 

[MacDracor]

Re: Die Off

My test strips don't measure ammonia directly, just nitrates and nitrites, but I've never had problems before. The Crawdad could be a factor, but the fish learned long ago to avoid him, and he never gets near them now.
I could buy that he's stressing them out except that a) I keep him well fed and b) they are all dying so fast. Since my original post, the Pearl Gourami has died, and he always stayed near the surface. I doubt he even knew there was a crawdad in there.

 

[Fishies86]

Test strips are very inaccurate. I would wither buy a liquid test kit (api is excellent), or find a fish shop that tests with liquid, just to rule out that possibility.

 

[Mr. Limpet]

My test strips don't measure ammonia directly, just nitrates and nitrites, but I've never had problems before. The Crawdad could be a factor, but the fish learned long ago to avoid him, and he never gets near them now.
I could buy that he's stressing them out except that a) I keep him well fed and b) they are all dying so fast. Since my original post, the Pearl Gourami has died, and he always stayed near the surface. I doubt he even knew there was a crawdad in there.

Yep, get a liquid test kit (API FW Master test kit is great) and start doing daily testing to figure out what's going on. High ammo burns the gills of fish, so knowing what level ammo you have is important.

 

[allaboutfish]

the crawdads like to eat fish and since you said he was eating one i think he's trying to kill them (i've had a crawdad also)