Saprolegnia? Columnaris?

Long story short, I had a fry tank and my fry have been nearly entirely wiped out in 48hrs. Upon removing the bodies, most of them look like they are fluffy. Since they died in such a short window, logic told me it's not decomposition yet. So I googled and it fits the bill of something called saprolegnia fungus. I did a bit of reading about that, mostly in relation to salmon. Then I typed in saprolegnia in aquariums and the first result was the dreaded C word. Is that what I'm dealing with?

Symptoms were non-existent. Fish were fine two days ago, yesterday I noticed they weren't "about" like they usually but put it down to hiding in the plant. This morning I went to do a water change on it and it looks like something out of a horror film. Almost all of the bodies are covered in cotton wool like fluff. It's hard to photograph as they are fry and it isn't visible out of water but I tried to take a photo of my oldest fry with it.

Firstly; does anyone have any idea of the cause? Their routine hasn't changed in a month. A new plant was added a week ago but it was from a group of plants, the rest are in my main tank which is displaying no change. The water parameters are 0/0/10 in both tanks. Both tanks are heated to 78. Both tanks get twice weekly 80% water changes with the same water. They are fed liquifry 2 and 3. The only chemicals put in the fry tank are prime and stability.

Secondly; what do I do now and what do I do with the survivors (2 fry and a nerite snail). Are the heater, filter and tank safe to use again? What about the plants? Should I scrap everything and start from scratch? What are the chances of the two fry surviving and will I ever be able to put them and the snail in my main tank or is there always going to be risk of infection.

Lastly; so far as I can think, the only thing that goes between the two tanks are my hands and one jug. What are the chances of my main tank already being infected without showing symptoms and is there anything I can treat it with at this stage?

I'm currently doing an 80% on the big tank and emptying out the little tank but I'll sit down and try and research when I'm done, in the meantime thank you guys for any help and advice.

ETA: sorry it posted before I was done, finished now. Fixed the comment.

ETA2: down to 1 fry and 1 snail; tank has been cleaned with hot water, everything but the heater has been thrown out just in case. If I had a spare heater I would have chucked that too but it's all I have. I've temporarily replaced the filter with an airstone while I order a new filter from Amazon. I've got one fry left and one snail, I'm going to QT them in this tank and if they survive, move them into the main tank, if they don't then they don't. Either way I think I'll take down the tank sooner or later and give up trying to save the fry and leave nature to it because it looks like I'm doing more harm than good saving them.

How long should I QT for in the case of a fungus? I can't see any on the snail what so ever. It's too soon to tell with the last remaining fry, it's very lethargic and hanging out at the surface despite the water being 100% new and oxygenated with an airstone.

Tried to edit the comment so it just shows the photo...

 

It sounds as though it was fungus. Saprolegnia is found in most aquariums and does not usually cause any problems. It is most commonly found in aquariums that have been lax on maintenance and water changes. Why it became so virulent in your fry tank is a mystery. At this point I see no reason to scrap anything in the tank. I would remove a gallon of water and put the remaining fry and the snail in there and clean everything with very hot water. (Except filter media) Rinse plants off well and remove dead or dying areas (this is one of the things that saprolegnia digest. A lot of plant decay would make their numbers raise) I have had no experience with fry since I try to avoid them at all cost, but I'm guessing they can be fragile. I have heard of several people who routinely treat eggs for fungus because they are susceptible, perhaps fry are the same. Sorry you are going through this. Maybe one of the breeders will see this and have more insight for you.

 

Honestly, the fry tank gets cleaned more often than my main tank. Twice weekly is my staple because I have two days off a week, usually one every 3-4 days so it's a nice steady schedule but as it only takes quarter of an hour to do the fry tank, if I have a spare 15mins, I'll clean it between big cleans.

They don't get live or frozen food so I can't see that being an issue and the fry food pretty much dissolves instantly into the water column, which is changed often so I can't see it being build up there. All the plants are alive and green, it's just a moss ball, something that looks like anubias and some anacharis clippings, nothing too fancy.

The only thing I can think of is I do leave algae to grow in there for the snail but he does a solid job of eating it. I only keep him in there to maintain a steady bioload for the cycle.

I'm really at a loss all round. I've got five fry that I couldn't catch in my main tank and they are alive and well not to mention the pregnant guppies and some Cory cats that have a reputation for being sensitive. However I'll admit these fry are from box store stock and are probably inbred as anything so yeah, maybe they were fragile.

Maybe overstocking? I did have quite a few in there but the cycle never showed any spikes and I assumed other stocking concerns like adult size/activity wouldn't come into play with fry as they would be rehomed as soon as they were big enough.

Either way, I think I'm going to scrap the tank after these 2 have finished QT in it because the 5 in the main tank are living happily so I'm not sure I need to go through the stress of separating them. I might use the space for a 5g betta tank or something like that. Breeding doesn't seem to be my forte.

 

I knew that the tank was kept clean. No one goes thru the trouble of setting up a fry tank who isn't meticulous when it comes to their fish. I was stating what usually causes the fungus problem. I can't see bioload coming into play either. I'm just stumped.

 

Sorry, didn't mean to sound like I was accusing you of saying that, I was more just bouncing thoughts about because I'm just as stumped.