Care for Silvertip Shark

Question
Hi, Karen.  I am really hoping you can help me here.  We have purchased a new 20-gallon aquarium for my son, who recently picked out six new freshwater fish from the petstore.  One of them was a silvertip shark, which I understand is really a kind of catfish.  I was assured that all of the fish would do just fine together (also bought two guppies, two neon tetras, and one platy).

I never did see him eat anything (we fed them all flake food), and after the first day or so, he began doing this pacing kind of swim back and forth across the back of the tank along the bottom, the next day moved to the top at the surface with the same pacing motion and would stop only occasionally to hang out nose-up under the surface by the filter.  Just 10 days later, he died.  

I had the water tested by the pet store, and it came out fine.  The water temperature was 79, which should have been fine...?  We've now replaced him with a new one, who was again very active the first day, but is now doing the same kind of hovering at the surface and pacing kind of activity.  This will be day three for our new silvertip, and I have yet to see him eat anything either.  

I'm tempted to return him to the pet store lest he doesn't survive with us, but I would love to know if there is anything I can do to make him happier.  I've heard different things from different pet store personnel, from freshwater is just fine to saltwater is best.  

Should I add some salt to the water, and would it really make a difference?  If so, will the other fish in be okay with that?  What food would be best?  

Any suggestions you might have would be greatly appreciated.  Thank you!

Answer
Hi Jenny,
Although it's hard to say exactly what caused the Silver-tipped shark's unfortunate ending. My first thought would be water quality in terms of high ammonia levels....And my next thought would be lack of brackish water.
Of course the former takes a bit higher priority because since this aquarium is relatively new, there is probably not enough biological filtration in the form of the vital beneficial bacteria whom make keeping aquariums healthy--possible. These bacteria are not existant in new aquariums and very slow stocking allows their colonization which is slow to grow and a typical cycling takes about 4-6 weeks.
Do not add anymore fish during this time. And feed fish very lightly once a day.

Even though your test results for the aquarium water have turned out fine it may be a matter of time until ammonia or nitrite spikes. If you should get a spike in either of these, immediately change 50% of the aquarium water to dilute the pollution.Always insure the replacement water is equal in that of temperature to your aquarium and is properly dechlorinated with a good water conditioner.

~*I would definantely add some aquarium salt to your aquarium. This may also be the factor in losing the sharks. They are well-known as brackish water fish which simply means kind of a mix of in between saltwater and freshwater.
Brackish water can be made by measuring 1 tablespoon of aquarium (not table) salt per 5 gallons of water. dissolve the salt beforehand in a clean (no soap residue) cup of aquarium water and when it's fully dissolved pour it in.
*NOTE: to avoid stressing the fish by a suddenly brackish aquarium, add half the dose at day 1 and then day 2 add the other dose to allow the fish to adapt and get accostumed to the salty water.
~Silvertip sharks can adapt to freshwater but I have found some brackish water fish don't do well at all when kept in freshwater. Silvertips can also actually be converted to a totally saltwater marine setup but they need to be acclimatized properly.

Please keep in mind Silver tips enjoy each-others company and a group is best...However, your 20gallon may not be big enough long term as Silver tip sharks can grow larger and longer than an  human hand at a maximum size of 12 inches or more... Typically around 6-8 inches as the norm.
~Your other fish should do OK with the salt as long as they are adjusted to it slowly. Although it's not preferred to keep a brackish aquarium for your neons, guppies, and platy.
Unfortunately it may be best for the Silver tip's sake to be returned to the petstore. I'm very sorry. But perhaps look into a smaller and more manageable catfish like the adorable Corydoras Catfish. These little fish are very cute and love to swim in schools, they are completely freshwater and won't even tolerate salt they are active little creatures always scavenging around the bottom for any food.
Just a thought.

But if you do decide to keep the Silvertip shark, please know that you must provide for his needs as he grows larger and requires continous brackish as well as very clean water.
Including a larger aquarium as he matures.

As for food. These guys can do Ok on good quality flakes but supplements are best in conjunction in the form of frozen foods like brine shrimp. When they are large they will accept pellets.

Silver tip sharks are a truly beautiful species. Although they are a wild caught and not farm raised catfish, when well cared for they truly provide a wonderful splendor and beauty all their own.

Best wishes, I hope this helps!
Let me know if you have anymore questions or concerns,
Karen~