Hello, New To Forums And Hobby, 75 Gallon Big Mix Of Fish. Who Is Kil

[chrisslowness]

Here is a list of fish in my tank, they all get along and the bigger fish fight sometimes but nothing serious.  For some reason if I put plecos in the tank they get murdered within a week.  And whoever is killing them is eating them not just killing them.  I also bought 4 of the pink kissing gourami, one morning 3 were totally eaten and one was still alive and is to this day and has grown half an inch since I put him in.  I just cannot figure out who the heck is killing the Plecos and why just plecos?
 
The population consists of:
12 Red robin fan tail mollies (less than 1" each)
6 Dalmation Mollies (about 2" each)
6 White Mollies (about 2" each)
6 Giant Danios (one is 4" others 2.5")
14 Black Skirt Tetras (They school up so well I had to keep buying them, they are awesome to watch)
6 Red Eye Tetras (they group up sometimes but never school)
3 Glow Tetras (these things die so easily I refuse to get any more no matter how cool they look)
1 Headstander 4"
1 Black Tail Barb (the #71###ing king of the tank at 5")
1 Rainbow Shark 4"
1 Iridescent Shark 4"
1 Skunk Botia 2.5"
1 Red Tailed Zebra Loach 3"
NO Pleco (was eaten on 3/26 I cannot figure out which fish is randomly eating others)
4 Drawf Guarami males 2" each
1 Pink Kissing Gourami 2.5" (bought 4, someone killed and ate 3 of them)
2 Red drawf crabs (one escaped and died)
3 Crawfish  (1 RIP Black Tail Barb attacked him (gets along with everyone in the tank, he bosses down any fish or other crabs that go after him)
4 Algea eaters (they grow so fast, like 3" each)
4 Dwarf Mollies (funniest looking little fish ever, all under 1")
5 Black Snails
2 Albino Cory (less than 1" each and going to get 4 more they like to group)
PLANTS:
Bamboo Plants
2 Banana Plants
1 African Sword
3 Crab Grass

 

[Lunar Jetman]

What are your water stats? Your tank is extremely over stocked so it could be that your water stats are high and the new fish are dying due to this.

As a rule of thumb you should have 75 inches of fish in a 75 gallon tank and I've just counted up over 125 inches of fish in your tank!!

It's possible your fish are fighting for space and any new fish have nowhere to go.

You need to re-home around half you fish and decide which shark you want to keep. I'd also research into the adult sizes of your fish before you buy anything to make sure it will ever be suitable for your setup.

 

[the_lock_man]

To answer your question, I would bet on it being the crawfish, fins and pincers don't mix, in my opinion.
 
However, I strongly suggest you rehome the iridescent shark as soon as you possibly can, before it becomes stunted. It might be a cute little 4" baby at the moment, it has at least 32 more inches still to grow, possibly more - in the wild they grow to nearly 1½ metres. It has NO PLACE WHATSOEVER in a home aquarium. Have a read of the Big Fish Campaign link in my signature area.

 

[TallTree01]

Holey moley!!! You're way overstocked.

12 Red robin fan tail mollies (less than 1" each) good
6 Dalmation Mollies (about 2" each) good
6 White Mollies (about 2" each) good
6 Giant Danios (one is 4" others 2.5") good
14 Black Skirt Tetras (They school up so well I had to keep buying them, they are awesome to watch) good
6 Red Eye Tetras (they group up sometimes but never school) good
3 Glow Tetras (these things die so easily I refuse to get any more no matter how cool they look) bad
1 Headstander 4" bad
1 Black Tail Barb (the #71###ing king of the tank at 5") bad
1 Rainbow Shark 4" good
1 Iridescent Shark 4" bad
1 Skunk Botia 2.5" bad
1 Red Tailed Zebra Loach 3" bad
NO Pleco (was eaten on 3/26 I cannot figure out which fish is randomly eating others)
4 Drawf Guarami males 2" each bad
1 Pink Kissing Gourami 2.5" (bought 4, someone killed and ate 3 of them) bad
2 Red drawf crabs (one escaped and died) good
3 Crawfish  (1 RIP Black Tail Barb attacked him (gets along with everyone in the tank, he bosses down any fish or other crabs that go after him) bad
4 Algea eaters (they grow so fast, like 3" each) bad
4 Dwarf Mollies (funniest looking little fish ever, all under 1") good
5 Black Snails good
2 Albino Cory (less than 1" each and going to get 4 more they like to group). Bad

All fish that are either too large, agressive, need bigger shoals or have other problems in this tank have a ' bad ' written next to them and need rehoming.

Welcome to the forums and I hope you get this sorted out quickly and efficiently.

 

[cpwebsite]

Your totally overstocked. I recommend getting rid of all of your fish and try and rethink your stocking and what you are planning on stocking in your aquarium. Make sure your aquarium is fully cycled, and do some research before you purchase fish again. Best of luck!