lighting problem

Question
We currently have a 20 gallon tank, containing three white skirt and three black skirt tetras, 2 bala sharks, a plecostomus, and 1 blue gourami.  We have a 15 watt full spectrum light for the plants and fish, but when we turn it on all of the fish excluding the gourami swim to the bottom, and STAY there.  They do not seem to adjust to the light, stay very close to the bottom of the tank, and swim very little.  They remain like this for the majority of the time the tank is lit (6-9 hours a day).  I know this is natural for the pleco given he is a nocturnal fish, but not so much for the others as they prefer well light tanks and seem to need them for health.  When the light is turned off, they fish instantly swim to the middle and top of the tank, and act much happier.  Is our light too strong for the size of our tank?  Or does their sensitivity to the light indicate some type of disease or illness?  We preform weekly 25 percent water changes and vacuum the gravel.  We also have a heater that maintains the temperature of 78 degrees.  The filter we use a Whisper, made by Tetra, intended for a 20-40 gallon tank. We have checked our water levels regularly and the only problem we have is hard water.  The fish don't seem to mind, but we aren't sure how to change this without using chemicals.  Ph, Nirtate and Nitrite, Ammonia levels are all good in the tank, and the fish seem fine, so I'm not even sure if the hard water should be a concern.  

Mostly we are wondering why our fish seem to not like their light when everything else seems right and they act very healthy and happy.

Thank you for any advice,
Calla


Answer
Good evening Calla,

I have to say, I have never heard of anything exactly like this. I'll offer my take on what's wrong and a suggestion.

Pet fish - some species more than others, although it seems to be a case of "every individual is different" - are indeed sensitive to photic shock. This is the same way we feel when we turn the bathroom light on in the middle of the night! The light simply stuns our eyes for a moment. This can cause the fish to become very pale and hide for a while, but staying on the bottom seems to tell a different story...

I believe that the inherent incompatibilities with the species are causing a temperament issue that is alleviated when you turn the lights off. The only nocturnal fish is the pleco, it's true. The white skirt and black skirt tetras are the same species (Gymnocorymbus ternetzi) just different variants, so they ought to school with each other. A school of six tetras is right on the money, however the bala sharks aren't the best of tankmates. First off, they grow large - beyond a foot, when fully mature. They are also naturally timid fish that feel better in schools. Certainly a duo is better than a lone bala shark, but that's a lot of fish flesh for a small to medium sized tank such as yours!

The bala sharks will grow slowly unless you do large partial water changes, in excess of 50% weekly, and feed frequently. (Once a day feedings and a water change of 30-40% weekly would be my recommendation.) In the long run, the bala sharks are best traded in for a species more suited to life in a 20 gallon tank. Another gourami might help make this one feel more at ease, although if this is the Trichogaster kind (also known as a three-spot gourami) and not the dwarf Colisa lalia, one is plenty, really, for a 20 gallon tank.

Just to clarify...I believe your lighting is not too strong for your 20 gallon tank - in fact, this is the kind of lighting I have in my 10 gallon tank. Live plants will need a light at least this bright, unless you have the indifferent varieties such as java moss, java fern and possibly hornwort which seem to do fine under low light. (Low light is considered 2 watts per gallon or less.)

The short term solution, in my opinion, would be to switch the full spectrum bulb for a softer bulb. I am very fond of the Penn Plax Aquari-Lux bulb, which I believe Walmart, Petsmart and Pet Supermarket all sell. It has a purplish to rosy tint which is very soft and dreamlike, in my opinion.

Another light I am fond of is the GE Sunshine bulb. For some reason, only the 15 watt variety seems to have an appealing glow. It is also a full-spectrum light. The bulb above costs about $10, the GE bulb about $6. Investigate for yourself! You can start here, for example, reading others' opinions:
http://cichlid-forum.com/reviews/

In the long term, consider trading in the bala sharks (which are beauties, I know) and perhaps the common pleco for a dwarf variety, such as the bristlenose plecostomus. This might resolve the problem without having to switch bulbs.

And, as always, whenever anything is amiss, test the water. Don't try to tweak the hardness of your water unless you are using reverse osmosis water. No other solution will be a permanent one, and stability and consistency are more important than a pH, harndess, etc. that is "ideal" or just so. Your fish will learn to adapt. Even if they never fully thrive as they might if they had their optimum levels, pH up or down and the like are stopgap solutions that do more harm than good, in my experience, both actual and in reading.

I hope that helps, take care!
Nicole