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Discussion Starter #1
I'm asking this question OBO a friend who - like me - keeps angels in plated tanks. In short, he recently had a number of angels die quickly. He had not changed anything recently in this well established tank, and did not detect any change in ph or nitrates. He is wondering what he should prepare to do differently before restocking.

More details: he has moderately to heavily planted 20g and 30g. The 30g only has DIY CO2. He stocks angels FAR more heavily than I do (and than I understand most do), but his tanks are always spotless, and in the past he has maintained angels for years.

This recent die-off occurred in his 20. About 1/2 year ago he bought about 6 dime-sized angels for that tank. They thrived and grew for 6 months until they were maybe 1/2 dollar size. One day they were looking fine, and when he next checked the tank maybe 20 hours later, 5 of the 6 were dead on the bottom. No visible signs of stress, infection, whatever.

He had not done anything different to that tank recently, and the params he checked were identical to his 30g and to what the 20g had been the previous 6 months.

So what kind of things ought he look into as he tries to figure out what happened. What types of questions out I ask him? What would cause such a sudden die-off?
 

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Some crazy things can go wrong sometimes too. I read of one person using one of those plug in air fresheners that does an automatic spritz every so often. I don't know how far from his fish tank it was but obviously not far enough. The spray found it's way into his water and killed the fish. Or live food gone bad? Or frozen food gone bad? Some contaminant in the air nearby other than plug in air freshener? Any toxic aerobic areas in the substrate where gas bubbles could have forced their way up? Anything on his hands that he can remember last time he had his hands in the tank? Sometimes it's hard to remember the normal things you do that might affect the tank and fish adversely. My elderly female dog is on a daily med similar to an antihistamine. She gets half a tablet a day. I use the same knife to slice the tablets and the zucchini for the fish. One night I had forgotten to rinse the knife off, there was no residue on it that you could see, I sliced a zucchini and put it in a 10G tank where I had a some small sterbai fry and pleco fry and watched them very quickly begin to float to the top of the tank. I was clueless as to what was going on in front of my eyes. I did an almost 100% water change and they are came around with that. It was after the emergency when I was beating my head to try to figure it out that I realized I had contaminated the tank with miniscule amount of that tablet.
 

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7 angels in 20 gallons is too much even if they are small. They won't grow right, get stunted at a small size, and die early. I worked in an LFS for a while, and we has someone come in at least once a week with dead angels because they had crammed a bunch of them into an unsuitable sized tank, and then wanted a refund for them. Angels are just one fish that doesn't overstock well. He should keep no more than 2 angels in that sized tank. Even if the bioload is fine when they are small, they will dirty the water more as they grow, and not have enough swimming room besides. (not to mention the aggression of so many adult angels--if they would live that long--in that little space!) Angels that are over six months old should be bigger than half-dollar size, so their growth has definitely been stunted by lack of space and probably poor water quality.

I would say it is probably an ammonia spike that killed them. Angels are fairly sensitive to those. Another consideration would be aggression--the one still alive killed the others. I've had that happen.
 

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Discussion Starter #5
Heck - I agree that he stocks way too heavily, and have told him so for years to no avail. But I would think that overcrowding stress or aggression would either not be as sudden, or would leave some sign.
I'll ask him what he tests for, and whether that includes Ammonia.
 

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My experience is that Angels once paired off are very agressive! I would only keep 1 pair of Angels in a 29 gallon or larger tank with dither fish. Cory's tetras (if they don't get eaten) etc...over stocking sounds like the issue!
 

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Discussion Starter #7
He says he tested - no ammonia spike.
 

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Could have been the bloat , is there a lot of fiber in their diet . ( Though it would be strange for them all to die of it so close together )
 
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