Fish Dying all of a Sudden - LFS Doesn't know why..

[TNFish]

I have a 20 gallon tank. Before the problems started there were 2 skirt tetras, 2 otocinclus, 2 endlers, 2 mollies, and 2 platys. LFS did three different water tests (when problem first started, in the middle, and just couple weeks ago) and everything was in normal parameters except the nitrates were 40 all three times. Filter before was Whisper Tetra 20 in-tank, new filter Aquaclear 30. Have had the tank for several years so its not new and has been cycled. Had both filters in the tank for a couple of days when switching filters like the LFS said. Do 50% water changes once a month, 25% in between. Only thing we put in there is a little aquariam salt and the tap water conditioner. Temp between 75 and 80 like always.

Around two months ago we had one oto die and the fish store said we should get the new aquaclear filter as it worked so much better. Switched the filters out and things were okay for a while. The nitrates stayed at 40 however. Then a week before easter, within 4 days span, we lost 1 molly and 2 platys (they all got skinny/wasted and settled at the bottom of the tank. Two of these were just purchased from said fish store 2 weeks prior. Water test done on Wed before easter came back the same. Other platy has been looking a little thin but still swimming normal. Just this evening we lost an endler. So we did another 50% change.

Could there be something with the filter since all this seemed to start when we changed them? We have had a fish tank of one kind or another for years. The tetras are old, and thankfully they seem good. We have never had this many die in such a short span. The LFS had no clue what the issue was. Any thoughts? Please help! Sorry for the rambling!

 

[TNFish]

UPDATE: Last platy died, skinny, then floated. That leaves the 2 tetras, 2 ottos, and 1 endler. Anyone have any thoughts whatsoever? So I need to try meds of some kind? There are no other signs of disease besides the wasting. I don't want to lose my angels!

 

[fluttermoth]

I'm sorry to hear of your problems.

Did you move the filter media from the old filter into the new one?

Do you have any idea of the actual numbers from the other tests? I'm afraid 'normal' isn't really informative to us.

It sounds like you've lost all your good bacteria; a week would not have been enough time for a new colony to grow in the new filter, so your tank has become 'uncycled', but without knowing the results for ammonia and nitrite, I'm just making an educated guess.

Do you know the pH and hardness of your water? Adding salt on a regular basis is not normally a good idea, I would advise you to stop doing that, especially now you've lost the mollies, the tetras and otos won't like it at all.

You didn't mention angels in your first post; how many of them do you have?

 

[Colin_T]

First thing to do if you ever lose a fish is to get a water sample for testing. Then wipe the inside of the glass down to remove the biofilm, do a 75% water change and a complete gravel clean. It's usually a good idea to clean the filter too, however, the new filter won't need to be done but the old one might.
Make sure any new water is free of chlorine/ chloramine before it is added to the aquarium.

Can you post a picture of the fish, sick, alive, dead , anything?
And what where the symptoms besides getting skinny and sinking to the bottom?

If the water quality is fine it could be hexamita, a protozoan infection in the fish's intestine. They tend to lose weight, do stringy white poop, stop eating and die within a few days to a week.

 

[stanleo]

LFS advise is notoriously unreliable. Two days is not near enough time for the bacteria to establish in the new filter before removing the old one. It should have been at least four weeks or you should have put the filter media from the old one in the new one. So that could be your first issue. How long had you had the first oto that died?

Nitrates can produce in the filter but more often than not the development of high nitrates is a result of insufficient water changes. How much and how often do you change your water? Most on here recommend 50% of the water once a week. The same day every week if possible. That could be another issue. The first oto could have died as a result of prolonged exposure to high nitrates though 40ppm is usually tolerated well by tank bred fish, wild caught fish like otos need pristine conditions.

You say you introduced new fish a couple weeks before this all started. That could be another issue. They could have brought a decease into the tank and the fish you already had did not have a strong enough immune system to fight it off.

Do you have your own test kit? Get one, don’t rely on your LFS. You didn’t mention your pH or water hardness or the exact numbers of ammonia and nitrite both of which can be lethal to fish. Otos and livebearers like your platys and Molly’s require opposite pH and hardness. Also, otos do not tolerate salt as well as the livebearers. They do, but at much lower levers. For instance, mollys are actually brackish water fish. They can thrive in fresh, brackish or full salt water. Post your pH, KH, GH, ammonia, nitrite and nitrate levels before you do a water change. But for now, do a massive water change, at least 80% with tamp matched dechlorinated conditioned water.

The salt brings up another issue. How did you introduce it to the tank? You should always dilute the desired amount of aquarium salt in a jug of tank water and introduce it slowly over a couple hours. Dumping it in at once can burn the fish and cause problems.

 

[seangee]

Do you have your own test kit? Get one, don’t rely on your LFS.

I agree. Something that is often overlooked is that being moved is already very stressful for fish, especially if the have been shipped a long way to get to the LFS. I always ask what the pH and hardness is in the tank that I am buying from. If the LFS can't tell me that they just lost a sale. Fish don't cope well with sudden changes in water, so they may need drip acclimation if your parameters are different from the shop. The fact that these fish are already very stressed explains why they are so much more likely to die shorlty after being moved.

Nitrate levels may be high for a number of reasons, and one of these is simply how much nitrate is in your tap water. If the fish are used to low levels and are moved into a higher concentartion that could just be enough to tip them over the edge. (For more info search for "old tank syndrome" - but it is not neccessarily down to bad maintenance).

Obviously we can't rule out any diseases in the new fish and changing the filter has compounded the issue but this is worth keeping in mind when you buy new fish.

 

[NickAu]

Do 50% water changes once a month, 25% in between

Hi

that is nowhere near enough, try 75% once a week.