re. feeding problems (Betta and Corydoras)

Question
Hi Brit,

I have several questions for you (I apologize in advance for the length, but I wanted to give enough detail to make it easier to answer).  I have a 10 gallon tank (and try to keep the water between 74 and 78), and I have a female Betta fish (which I got a few months ago), and 2 panda corydoras (cory cats) which I bought about a week ago.  I'd been feeding the Betta two little 'TetraBetta Floating Mini Pellets' since I got it a few months back, and this had been very well-received by the fish.  When I got the corydoras, the person at the pet store recommended 'Nutrafin Max: Sinking complete food tablets for bottom feeders and invertebrates'.  These are fairly large (compared to the pellets I feed the Betta)...comparable in size to a little vitamin C pill.  The salesperson said that I should give the 2 corys a single tablet a day (to share between the two).  This new feeding situation is creating several problems (I should note that, overall, the corys and the betta seem to get along very well, although the corys are naturally frightened of the betta as she's larger than them).

So, I've been continuing to feed the betta the 2 floating pellets each day, and then, after I've done that, I've been dropping in the tablet for the two corys.  What seems to happen now is that the betta notices the tablet well before the corys do (no matter where in the tank I drop it), and the betta dives down and starts nipping away at it.  The corys eventually figure out where it is, but if the betta is in the way monopolizing it (as is often the case), they won't approach.  It's hard to tell whether the betta is actually eating much of the tablet or just picking at it, because lots of bits of it break off and then get sucked up by the filter, it seems (which creates another problem because the inside of the filter, and indeed the water in the tank as a whole has quite a funky smell to it which just appeared after I've started feeding the corys with these big tablets).  At the same time, I think the betta must be actually eating (not just picking at) at least some of the corys' tablet each time, because these last couple days when I've been feeding it its pellets, it gets the pellet in its mouth and then spits it back out (several times over), before either eating it, or just letting it drift off and waiting for the corys' tablet instead.  So, I'm thinking maybe it's getting its fill on the corys' food and has no appetite for its own.  

So basically my concerns are:

1.  Are the corys getting enough of their food tablets, given that the betta seems to be picking at and/or eating so much of them, and given that the many bits that fall off the tablet are then either being sucked up by the filter or being scattered under the marble substrate?  If the corys aren't getting enough food, how should I deal with this?

2. Should I continue trying to feed the betta its pellets, when it seems to have more interest in the corys' tablets?  

3. The smell in the tank and the filter is a concern, not just for the fish, but because in a one room apartment it's starting to get somewhat obnoxious.  I attribute this smell to the Nutrafin tablets I've been giving the corys (the fact that the tablet breaks up before, and as, it's being eaten, with bits becoming lodged under the gravel, and much of it being sucked into the filter as well, I think).  I'm wondering how to handle this:

a) Is there a type of food for bottom-feeders like the corydoras which is more along the lines of the pellets I'd been feeding the Betta (which are small already and do not break up and stink up the water) (of course, I still plan to do water changes, but should not have to do it every other day to avoid an unpleasant smell in there)?  I'd really appreciate any recommendations.

b) Is there a type of filter pad which can be reused an unlimited number of times so that, IF the corydoras does actually need to eat large tablets like this that break up and make the water and filter smell, at least I'd have a way of cleaning the filter regularly without having to buy a new cartridge often?  (My filter is a Tetra Whisper Power Filter, and, although the package for the Filter Cartridge says it "removes odors and discoloration", it's not doing much of a job removing odors!).  

Thanks in advance for your help with these questions.  Again, I'm sorry the message is so long.  I just wasn't sure how much detail to provide, so I thought I'd include everything I could think of.   I really appreciate your advice.

Sincerely,

Ken

Answer
Hello Ken,
I appreciate the detail in your question. I will start off by saying that the only filter I know of where you don't have to replace anything quite so often is the biowheel. It is an excellent filter, and the biowheel itself aerates the water, as well as the beneficial bacteria that live on it, so it will definitely help keep your tank healthy. Unfortunately, I am not a good judge of odor, as I have no sense of smell, but I haven't heard any one else complain, so there is a plus.
Next, the easiest and most obvious way would be to separate these fish into different tanks. I understand the tank may look "bare" without the betta, but truly these fish would never meet in their natural habitats, and it is obviously creating more drama than any fish keeper needs in the tank!
However, if you really want to try to keep them together, you might be able to help solve the issue by doing a few different things - For one, add more decor to the tank, especially low, small decor with plenty of hiding space for your corys, and find a pair of long thin tweezer like appliance (such as tongs) and try to place the pellet directly on the bottom of the tank, just PRIOR to feeding your betta his pellets. You might also get a veggie clip and add a small slice of cucumber or zucchini to your tank for the corys to nibble on. It is important to feed your fish a varied diet. No one food contains all the nutrition that a fish needs. By feeding a variety of foods you fish will stay healthier, be happier and grow much quicker. Just be careful not to overfeed! Most catfish love this treat, and you can do this a few times a week, which may ease your mind about whether your corys are eating - you can see bite marks and nibbles in the cucumber!
If this doesn't work out for you, then you may just have to separate them. You can find other small, pretty fish to put into your ten gallon, and place the betta by itself in a five gallon, with a tank heater, and maybe a snail or two? No filter needed, with regular weekly water changes. In your ten gallon, you'll want to add no more than 2-3 small fish, that grow to no larger than 2-3 inches, if this is the route you choose. One I like to recommend is the sparkling gourami, which is very pretty and rather small - usually growing no larger than 3 inches in captivity.
As far as food goes, you have many choices out there. Wardley Spirulina Discs: These, along with Algae Wafers supply most of the nutritional needs of any of the bottom feeding fish. However, a lot of other fish like this as well. You really have to find a food that is good for your corys, that your betta will not eat. O.S.I. Spirulina Flakes: The flakes enable the other fish that don't care for the Discs to get some Spirulina as well. Spirulina is a necessary part of a fishes diet. You might try breaking the discs into pieces, mixing it with the OSI Spirulina flakes, and putting it into the take at once, so the betta can get these flakes which should float temporarily, while the corys possibly get the pieces of the disc which should sink faster. If you have more than once kind of fish, mixing and matching food until you get a good combo is really the only way to go, especially as, as I said before, variety equals happy healthy fish!