Unsuccessful Tank

[Rogue Scales]

I have one 20 gallon tank in my living room that is consistently unsuccessful. It has a heater set to 78 degrees, a sponge filter and hang on back with sponge instead of carbon filter. This tank has been set up for a year with consistent normal parameters. My other tanks in my bedroom have not had the same problems.

Here’s what I mean by unsuccessful. I have had white clouds, cpds, bettas, platys, snails, plants including moss, octopus and crypts in the tank and rotated as I noticed them not thriving.  The fish spent most of the time hiding and while they ate, I noticed they were getting skinny. I had groups of 8 (except the betta). This was particularly obvious with the cpds. The snails would die off within a few weeks of putting them in.  The plants would be growing and green for about 2 months then suddenly die back completely or to less than half the leaves they had.  I haven’t had an algae problem at all in this tank.
 

I have done up to 50% weekly water changes when I noticed a problem. The fish were quarantined prior to going into the tank and again before moving to a new tank when I noticed they were struggling.  Plants have gotten easy green and root tabs  with no improvement.

At this point I feel like I should completely tear down the tank, clean everything and restart.  
 

Does anyone have any ideas what could be the cause? Better recommendations on what to do other than tear down?

[TheDukeAnumber1]

Something that kills snails, hurts fish and plants, all while your other tanks are ok...

I would start trouble shooting by identifying what is different in this thank compared to your tanks that dont have this issue. My first guess would be that something toxic is leeching out of the substrate, but it would be good to know what the other setups are too.

[Rogue Scales]

I’ve attached a couple of pictures. I bought a big bag of gravel and have used it for every tank so substrate is the same.  The plants are all from the same parent plants.  
 

Today’s parameters are. 
tank in question-

ph 7.0

ammonia 0

nitrite 0

nitrate 50

hardness 150

buffer 40

control tank-

ph 6.8

ammonia 0

nitrite 0

nitrate 175

hardness 150

buffer 40

[sudofish]

Something in the paint on the spongebob ornament leeching into the water column maybe? Just a wild guess. There isn't a possibility of a spray of some kind whether cleaner or whatever accidentally getting in to the water is there? No arms have gone in the water with sunscreen on etc..

[quikv6]

I know the control tank isn't the one in question here....but Nitrate at 175.....wow....seems very high.

[Guppysnail]

was the tank in question bought new? If not prior to you purchasing they may have used a cleaner or meds that soaked into the silicone and is leeching.  I agree with the sponge bob thing being questionable as I have read on occasion the paint on some decor over time leeches toxins

also the room it’s in could be the issue.  Loud tv people lots of activities causing excess vibration. Being close to the kitchen where cleaners are sprayed...those are 2 reasons I cannot have one in my living room. My hubby always has the tv on earsplit level.

Edited June 28, 2021 by Guppysnail

[Griznatch]

Have you tried lowering the temp slowly to around 74? Many of the fish you mentioned do better at lower temperatures. Not sure if that would aggravate the high nitrate levels you have

[Rogue Scales]

Thank you all for your responses!  I’ll try taking out the artificial decorations, give everything a thorough wash, replace the gravel and plants.  I sealed this tank myself and several of my other tanks that have no issues.
 

Thanks for mentioning the high nitrate levels.  All my tanks end up with high but stable nitrates after cycling.  Even with low stocking, light feedings and weekly water changes, I end up with high nitrates.  
 

I have tried various heater settings. 78 was the setting for the betta as the only resident.

I may shut this tank down all together and plan on relocating it when I have fish again to put in.

 

thanks again!