29 Gallon Tank Disappearing / Dying Mollies Mystery??

Hi all! I will try to keep this as short as possible, but I really don't know where to turn. Thanks in advance for your time & help!!:

Aquarium Details:

1. Tank - 29gal, 1+ yr life, filter & heater, temp 78-80F
2. Fish Stock - 1 Adult Platy Red Wagtail (store bought 2-3"), 2 (of 7 total) Young Adult platinum mollies (born 10/20, 1-2"), 2-4 Baby Platinum Mollies (born 9/21)
3. Maintenance - 2x/month, 20% water changes, Conditioner & Quick Start added to new water, Vacuum substrate during cleans
4. Parameters- I use the API test kit & Tetra test strips (Below readings are as of today-- though have not changed throughout the past few months):
   1. Ammonia - 0.0ppm
   2. Nitrite - 0mg/L
   3. Nitrate - 0mg/L
   4. ph - 8.0
   5. Hardness (GH) -150 ppm
5. Feeding - Fed once daily, Hikari Micro Wafers (for Tropical Fish), each fish eats ~5-7 pellets. I will alternate with Aqueon Tropical Flakes. I have fed them the same way since for over a year without problems. Tried feeding them blood worms once but got queasy, lol!
6. Illness & Symptoms

I had a molly (store-bought) give birth to 7 babies last October '20 before dying shortly thereafter (swim bladder, other fish were fine). I raised the babies without any problems to the size/age of adulthood, ~1 year old. The largest of the 7 (female), gave birth to her own babies at the beginning of this month. Around that time (a little before), I have been having mollies disappear and/or die on me. There is a strong flow with bubblers (no lack of oxygen). After the first death, I began treating the water with Stress Relief & a small amount of Aquarium Salt. I found the molly dead, so I'm not sure how it was acting before death. I did have another die, which I witnessed throughout. He was just resting on the substrate, visibly weak. He would eat the food that sank down to him, but could not swim well. [NOTE: As mentioned, I had a fish die of swim bladder disease. This death did not seem similar, as he had no problem staying upright. He just looked visibly tired.] The dead bodies of the two fish I found did not appear abnormal (no spots/fin rot/etc-- I have pictures if helpful, but did not want to put their resting souls on blast).

3 of the other 7 fish have gone missing. By missing, I truly mean missing--- I have no idea where they are. I searched in the whole aquarium (filter, decor, substrate) & even looked on the floor around the tank. There have been no spikes in ammonia/water quality decreases to indicate the decaying bodies. I've checked everywhere to no avail; I am truly am baffled. I presume they are dead, as they have not been spotted in ~2 weeks. Note: they did not all go missing at once. But having a missing fish was not an abnormal occurrence before this-- he would usually be just hiding-- and I've never had more than one 'missing' at once or for long. That leaves me with the platy and 2 of the 7 mollies ( + the new babies)-- the weird part is that the remaining fish are very vibrant in color and have no noticeable health problems. They eat and act normally as before. The only thing a bit weird is that they get scared easily and will dart across the tank, almost erratically. I feel like there is something wrong, but the water levels seem fine & even the babies have been growing normally and seem healthy (I have not separated them). I even think the female might be pregnant again.

I know stress can be a cause for unexpected fish death, but I cannot for the life of me think of a stressful event. I did move the fish from one house to another (short trip) in the beginning of June (4 months ago). They seemingly adjusted to the move quickly and they even ate that same night. I can't imagine that the stress of the move would come to kill them all 4 months later-- though I may be mistaken.

I am reaching out here, as I am baffled by the situation: on one hand, I have super healthy looking fish and babies that are growing. On the other hand, I have disappearing and dying fish that don't seem to have any abnormalities. Please if anyone has any advice, ideas, or similar experiences, please share! I am desperate to find out how to help my fish!!

 

Did you check the filter for the missing mollies?

 

Did you check the filter for the missing mollies?

Thank you for the reply-- Yes, I did. I will add that to my original post.

 

Thank you for the reply-- Yes, I did. I will add that to my original post.

Ok just checking. Often the filter is overlooked when there are fish missing. I suppose it is possible they died and the other fish ate the bodies. Or cats got them.

 

Ok just checking. Often the filter is overlooked when there are fish missing. I suppose it is possible they died and the other fish ate the bodies. Or cats got them.

In regard to the deaths-- any ideas? That is my main concern, as this is seemingly out of no where. Or just keep monitoring everything? I was considering if I should do a very large water change perhaps? But don't want to stress them out more (if stress is the cause). Thank you!!!

 

In regard to the deaths-- any ideas? That is my main concern, as this is seemingly out of no where. Or just keep monitoring everything? I was considering if I should do a very large water change perhaps? But don't want to stress them out more (if stress is the cause). Thank you!!!

Personally i would change it to 1 water change a week at 50% or around there. My fish seem to struggle a bit in my 29s if i don't do at least a 50% change every 2 weeks.

 

Personally i would change it to 1 water change a week at 50% or around there. My fish seem to struggle a bit in my 29s if i don't do at least a 50% change every 2 weeks.

Thank you! I was concerned about changing too much water at once, but hearing that makes me feel better!! I will try it out. Can't get worse than the status quo. Thanks!