Question about a tank bully and a filter.

Question
I just recently bought my first aquarium, a 10 gallon.  I decided to cycle it with fish, and bought one platy and one swordtail.  Not knowing anything about what I was doing... I bought the swordtail with ich on it and it eventually died.  I replaced it with another swordtail and so far no sign of ich on either of the two fish. The problem is that this new swordtail is NON STOP chasing around my platy.  The only time it is not chasing around the platy is when it is sleeping.  Is there anything I can do to prevent or change this?  I am thinking of buying a molly or betta soon also. Would this help?  Also... I have had the tank running for about a week and a half, and i know i will be replacing the filter eventually.  It is a whisper 10.  Would I kill off too much bacteria if  just replace the actual filter and carbon and keep the plastic cartridge that it goes on? Any help is greatly appreciated.... and thank you very much in advance!!

Zak

Answer
Dear Zak,
What you are observing with your swordtail is typical of male livebearers. He is trying to breed the platy I am most certain of. Male swordtails can be relentless in this sort of activity and this is why it it best to have one male to at least 4 or more females to avoid the male concentrating on any single female too much. Interesting that Swordtails will in fact hybridizes with similar livebearers like platies. This happens very often. Overpersistant males can really stress out females.

Because you shouldn't add anymore fish (since your aquarium is only a week and half running) your aquarium has probably not yet cycled or established a good-working bacterial colony. To prevent stress on the platy's part, you can seperate the swordtail by placing him in a large "breeder" net designed to hold pregnant platies and other livebearers while they drop their fry. These fine cloth box nets hang on the side of your aquarium and allow water circulation. Although it is unsightly to many aquarists, this may be your best option to keep peace in your aquarium.

I wouldn't replace the filter cartridge just yet. Especially since you are just starting out with cycling your tank. Don't worry about replacing it until at least your tank cycles which is indicated probably as you know by a consistant ZERO reading for ammonia and nitrite and a moderate reading of the safe nitrate. Even then take a pair of scissors and cut a large strip out of your old and dirty filter when it comes time to replace it. Put the new filter cartridge in, and place the big strip of old material right next to the new. This will "seed" the new cartridge with beneficial bacteria and should give it a jumpstart to developing a new colony of the fresh pad. This should also avoid any severe depletions of your bacterial colony.

Please don't add anymore fish just yet. Most aquarium's do not cycle in a week or less and I feel you should stick with your current little fish and wait until you are sure your ammonia and nitrite readings are consistantly Zero before you add anymore fish. Remember slow stocking it best.

Back to the first problem, once your aquarium establishes, you can add a couple more female platies or swordtails to help avoid the single little platy from becoming too stressed. And Mr. Swordtail can go free from his little net holding area. Remember you will have some bickering with the male breeding with the females. But it shouldn't be on a grand scale with a good size group of female platies/swordtails to help keep it 'even'.

I really hope you can establish peace in your aquarium!! I hope this helps and feel free to write with anymore questions...

Best wishes and happy fish-watching!
Karen~