Say It Aint So

I can't believe I'm writing this. An unknown killer has again killed my fish and I'm getting ready to throw in the towel on my breeding operations. Here is what just happened and at the end of this post, I'll share links to this EXACT same thing occurring to other species of fish in other tanks.

Tank Info:
20 Gallons, established for 1 year.
Inhabitants: Roughly 20 1/2 inch long fry - my first batch of F1 Pelvicachromis Kribensis "Moliwe"
Temp: 83F
Water Quality: pH 7.2, kH 80, gH 100, Ammonia: 0, Nitrite: 0, Nitrate <10
NO recent changes/additions to the tank.

Situation: I left on a 2 day family vacation with my kiddos. When I left, the fry were vigorously eating and swimming around, living their best life. I came home today to a mortality rate of 80% and climbing.

Symptoms: None - except that those that are left alive seem sluggish and the tips of their fins are foggy white (excess slime coat)? They are not gasping for breath, itching or anything else.

I immediately did a 50% water change.

Backstory: This exact same thing has occurred to me two times before - once in a tank full of Ram Cichlid fry (3 months ago) and once to a breeding pair of cockatoo apistogramma (1 year ago). Both times I was unable to determine a concrete source for the issue. I was previously making my own RO water at home for these aquariums (our local water is as hard as concrete) and it was thought that possibly that somehow the resins in the filter contaminated the water and caused the fish to be poisoned. Since I didn't have a better theory, I've begun buying pure RO water and using that in ALL of my tanks and supplementing with rain water when we get a good rain.

I do the EXACT same maintenance schedule for all of my aquariums and I have other aquariums running right now with healthy fish. A 20 long house 15 cockatoo aristo (grow out), a 20 long with the breeding pair of Moliwe and 1 month old fry and a 10g with a pair of cockatoo aristo and their fry (looking to get them in a larger tank soon). These fish have all had the same care taken of them - but they aren't dropping like flies.

Here are the previous scenarios:
Killer Tank Strikes Again
Poisoned?

I have lost a lot of money and time due to whatever is the cause for these deaths. Please someone help me before I give up!

My fry were doing this as well... They just kept disappearing and only at night. The only thing that kept them alive was moving them to a separate tank... That's the only way mine are still alive.

Rocky998 said:

My fry were doing this as well... They just kept disappearing and only at night. The only thing that kept them alive was moving them to a separate tank... That's the only way mine are still alive.

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maybe some predatory pests at night?

Yah that's what i was thinking... Kinda weird I never see them though. Or it could be the adult fish getting a snack lol

Sgooosh said:

maybe some predatory pests at night?

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Rocky998 said:

My fry were doing this as well... They just kept disappearing and only at night. The only thing that kept them alive was moving them to a separate tank... That's the only way mine are still alive.

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Sorry you've experienced that.

I believe that my situation is much different though - so I'm hoping to figure out what I am doing incorrectly.

If the fish are just disappearing they are being eaten.
If they're floating then I'd put it down to the water.
RO is pure to the point of it having no mineral content whatsoever and rainwater is also largely devoid of minerals. If you're just dumping them in without addition of trace elements they're going to suffer badly.
I have rainwater myself and use it alongide treated tapwater which was very hard with a ppm of around 460.
To reduce it down to accpetable levels I initially mixed it with supermarket 5ltr bottles of spring water. These have all the usual trace elements in it.
Since I now have a rainwater barrel I also use that to further decrease the GH and pH levels but I won't use it by itself.
Have you tested for GH, pH and KH? If not then please do and let us know the results.
Ah, sorry. I see you have posted the GH etc.
So is there something else you're putting in the water? Anything at all including infusoria. Something's not right with the water as far as I can ascertain. Since it's only happening to this tank, and to other fry in the past I'd look deeply as to how they are being fed since that appears to be the only different thing between other tanks.
Oh, how big/small are the fry? Pictures ----

what did you do to the tank the day when you left?
do you buffer the r/o water?
was the pH low when you got back?
how often are you doing water changes on the tank and how much do you change?
has it got a filter on the tank?

I would buffer the water so the GH is around 80-100ppm.

I will not go, turn the lights off
Carry me home

Sorry, with that title I couldn’t resist

Lynnzer said:

So is there something else you're putting in the water? Anything at all including infusoria. Something's not right with the water as far as I can ascertain. Since it's only happening to this tank, and to other fry in the past I'd look deeply as to how they are being fed since that appears to be the only different thing between other tanks.
Oh, how big/small are the fry? Pictures ----

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I do not add anything else to the water. They are fed BBS and a commercial product called "Golden Pearls" Size 6 - which are both foods I have used before and am using in other tanks, such as the tank with Cockatoo fry in it and the second tank of Kribensis fry. Fry are about 1/2 inch long.

Colin_T said:

what did you do to the tank the day when you left?
do you buffer the r/o water?
was the pH low when you got back?
how often are you doing water changes on the tank and how much do you change?
has it got a filter on the tank?

I would buffer the water so the GH is around 80-100ppm.

Click to expand...

On the day I left, I simply fed them the same amount that I always do and then walked away. I used to buffer my own water, but it seems with gravel in the tank, the tank naturally buffers (meaning my pH was close to 7.6 when all was said and done). When I do a water change there is a minute pH drop (since the RO is 7.0 and the tank is 7.2) but it has never seemed to caused issues prior - I use the same method for all aquariums and the same water.

This tank has a sponge filter and I do weekly 25-30% water changes.

Look into oodinium - velvet.

That parasite's a hard to spot slaughterer of well fed fry in soft water.

Pictures and video of the fish?

If you only do a small water change once a week, there could be a build up of external protozoan parasites like Costia, Chilodonella or Trichodina. These can kill fish quickly and love dirty tanks.

If you aren't washing the tank out between rearing batches of fry, and only doing a 25-30% water change once a week, then the tank could be bad (full of harmful pathogens).

Rearing tanks should get at least 2 or 3 big (50-90%) water changes every week, and they should be washed out after the fry have been removed. The filter can be cleaned normally but the tank and gravel should be washed out with tap water to make it nice and clean for the next batch.

GaryE said:

Look into oodinium - velvet.

That parasite's a hard to spot slaughterer of well fed fry in soft water.

Click to expand...

I've dug into this a bit - I don't believe it's the culprit, but it's good to know about this condition. I've only ever seen "velvet" on fish such as black mollies.

Colin_T said:

Pictures and video of the fish?

If you only do a small water change once a week, there could be a build up of external protozoan parasites like Costia, Chilodonella or Trichodina. These can kill fish quickly and love dirty tanks.

If you aren't washing the tank out between rearing batches of fry, and only doing a 25-30% water change once a week, then the tank could be bad (full of harmful pathogens).

Rearing tanks should get at least 2 or 3 big (50-90%) water changes every week, and they should be washed out after the fry have been removed. The filter can be cleaned normally but the tank and gravel should be washed out with tap water to make it nice and clean for the next batch.

Click to expand...

It looks like out of 20-25 fry, we have two survivors who are eating and swimming normally, but showing remnants of the extra slime coat (edge of their fins). I'll have a picture up in just a bit.

I can definitely increase my water changes - perhaps that will resolve the issue. I'm not sure if it matters when discussing harmful pathogens, but every water change that I do includes a gravel vacuum. I clean every square inch of gravel in the tank - which in my mind (but maybe not backed by science?) was removing a majority of the places where these harmful pathogens could be living.

This tank has not had fry in it for a while (it was holding a few guppies to keep it cycled) so at least for now, I would think the issue is not related to previous incidents.

Here are the best pictures I could get: