There are a few things we'd need to know to figure out what what happened.
Do you use dechlorinator to condition the water used for the tank?
Do you have a filter and what kind is it?
How big is the tank?
Did the fish exhibit any strange markings before they died?
Did you put anything into the tank that may have had toxic substances on it?
Often the problem with new tanks is that a colony of beneficial bacteria hasn't had a chance to develop. These bacteria break down the fish poop or uneaten food converting that to less harmful nitrates.
Try to answer the above questions, and you may want to take a sample of the tank water, if you still have any, and have the aquarium store check it for uncycled waste products like ammonia, nitrites, and nitrates, as well as pH (the level of acidity to alkalinity)
These test kits can also be bought so that you can always easily check the water for high levels of toxic waste products. There is usually a period of time after you set up and introduce fish where the colonies of beneficial bacteria haven't multiplied to the level necessary to break down all the waste.
Once the bacteria have colonised the filter there should be no problems with keeping the water clean for fish.
This may be a stupid question since it hasn't been mentioned. But it sounds like you put two male Fantail Bettas together? If so, they killed each other.
fantail is also a description of a kind of goldfish....it sounds like once they realized fish keeping is slightly more complicated than just throwing any fish into some water in a container they gave up...doesnt look like they've checked back here at all.
its terrible really...those tanks are often advertised as "perfect for goldfish" ...now that I think of it there are alot of fish that have fan-like tails arent there? they could have even been talking about a kind of guppy? hm... either way...poor fishies. It reminds me of when I was little and bought a little feeder goldfish...filled a small fish bowl up with tap water and put him in...I was so excited but he died over night. I think i named him Astro. I had no clue what i was doing...I wish someone would have told me.
All animals should require the prospective new owner/parent to undergo training appropriate to the species and be licensed before a purchase/adoption can be made. Think of the suffering this would avoid.
I was fantasising about having a small public aquarium with an aquarium store attached to it. I imagined school groups and parents bringing their kids and such, and I thought of giving discounts if the kids, or adults, could watch an instructional video or lecture/presentation and then pass a quiz about keeping aquariums. People are motivated by a discount, and I thought this would be a good idea for coercing people into learning how to care for an aquatic ecosystem.
I guess it depends on what they're buying. If they're buying a $3.00 Betta to put in a 2 oz. vase they already have, they might not care about the discount. But I do like the creativity.
I saw some huge glass containers at a local liquidator store that would have been PERFECT for bettas they were HUGE and really nicely shaped (probably for filling with decorative stones or something and would fill up a corner of a room nicely)....could even accomodate filters and heaters. Unfortunately Im clumsey and the lovely things probably wouldnt make it much further than the store exit in my hands.
