A gravel vac can work on sand but it will be harder to use although you can get a thing called a syphon which is basically a gravel vac designed for cleaning sand; you should clean the sand once a week making sure it is stirred up thoroughly and then do a water change depending how much water was taken out by the vac, 30% of water taken out and replaced with new water and adequete dosage of dechlorinator/water conditioner should be more than adequete for keeping good water quality once the tank is cycled.
Alternatively you can just thoroughly stir up the sand with your hand making sure it is realy stirred up and then do a 50% water change and leave the filter to sort out the rest and you can get away with this- i do this alot in my smaller more heavily planted tanks where getting the vac in without knocking over everything is imposible and i have managed to maintain good constant water stats with no problems with this method.
On the subject of buying fish though, i think one of the most important aspects of fish keeping is taking full responsability in every area of it, and i suggest you learn how to spot out unhealthy fish yourself when buying them without the stores staff helping you, this is a very usual thing to know how to do.
Some things to look out for when buying fish are(particually livebearers);
Before buying any fish, you should inspect it closely. From an animal's external apperance, you can detect many problems and diseases. Particulary examine the body, gills, fins, eyes and skin.
Body: Any healthy live-bearer's abdomen should look convex, when viewed in a profile. The female usually looks more convex then the male. These fish have a "chubby" look to them. This should also appear in females that have just given birth, even though they may look very slender. All other fish should appear well-fed.
Be careful of fish with protuding scales, and bloated bellies! Most times, if not all times, these fish are incurable.
A large head, that looks disproportionate to it's body, is usually a sign the fish has undergone long hunger periods. This doesn't mean the fish will die, but it shouldn't be used for breeding.
Gills: Healthy fish breathe slowly, although they breathe somewhat faster in a densely populated tank. As the fish breathe, they expose the gill cover. This should appear a pale reddish color, in healthy fish.
Fins: Missing or partially developed fins are ALWAYS a bad signal. Frayed edges on the fin, are usually the sign of a disease, although there may be other causes.
In a healthy fish, the fins should visably stick out from the body. The one exception is the dorsal fin in some species.
A fish that clamps it's fins, and maybe rocks from side to side is definatly not feeling well, and may easily get a disease.
Eyes: The eyes should appear clear, and never protrude un-natuarally from the head.
Skin: The skin should not show any white spots, mold, fungus, or white film. The scales should hug the body, and look smooth. Be sure to examine the tip of the mouth with extra care, to be sure there is no white film.
Another sign to look out for when buying healthy fish is avoid it if it seems to hang around on its own near the bottom of the tank alot as this is a common sign of a sick fish. Also avoid getting a female livebearer that is heavily pregnant(although this can be hard to find, particurally in guppys) because not only is the move from the fish shop to your tank twice as stressful (i.e she will be more likely to abort her fry, become ill and/or die). The other reason is if there is a sudden difference in water stats like ammonia in coming from the lfs tank water to yours, this can cause birth deformitys in the fry, cause still born fry and/or miscarriages.
Some deseases are more infectious than others and practically all lfs's will have one sick fish or another, but avoid buying from stores which have more than 4 fish dead in them.
Also there are some realy important deseases to look out for and avoid in fish;
a. Whitespot or somtimes known as Ich or Ick, the fish is covered in numerous white spots about 2mm in length is the main symtom. Avoid fish from any tanks which have any fish with signs of this desease- even if there are seemingly un-affected ones these fish will most likely be carrying the desease and it is highly infectious and can take a long time to treat- left untreated or un-adequetely treated and the desease is lethal and can decimate entire stocks of fish.
b. Red or inflamed bums on the fish- this usually indicates internal parasites and these are very hard to get rid of even with medication- very thin and not active looking fish also can donate this or internal bacteria which is also just as bad.
A good site with lots of pictures of fish deseases to help you indentify them and treat them is;
http
/www.fishpalace.org/Disease.html#Popeye
On the subject of your cow fish, a good site for info and pics of catfish/plecs is;
http/www.planetcatfish.com/core/index.php
Just go to to Cat-eLog and they'll have all catfish available to fish keepers and as much ifo that is currently known about them- they have thousands of fish listed to say the least.
My only other thing i can suggest right now is water testing kits, make sure you have ones that test for ammonia, nitrates and nitrites and test you water on an everyday basis while you are cycling your tank, after it is cycled just make sure you test the water at least once every week
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Testing your ph/gh/kh may also be helpful so you know these stats are in your area and will help you decide on more fragile fish in the future although i strongly advise not to use any ph alterers/boosters as these are most often unesarsary for the fish and can cause many complications and stress- basically not worth it unless you have a fish that is realy specific about these things and you know how to use them properly.
If you have anymore questions just post on here
/www.usaguppies.com/images/Japanese_Medusa_Galaxy.jpg
/www.ccg.org.br/images/guppy12.jpg
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