i need some help

Question
QUESTION: i have a 30 g. tank with 2 med Oscars, we had recently transferred our tiger Oscar to a different 30 gal. with an albino Oscar and they are the same size both eat pellets and live comets. but my tiger has seemed to be picking on the albino so a put him back in with the 1 silver pacu and 2 small red beelied piranha ( they were together 7 months before i took him out 1st time) we ended up getting a bad case of aqua algae (only in water not sticking to anything) and the piranha started to attack him (never did it before) so we switched him into the other tank again i know it isn't a very healthy thing to do to my pets but i love him dearly and don't want him to be fish food!!! but now we have another problem he is missing the bottom lip and my albino is picking on him. should i let them battle (will they start to get along) or get yet another 30 g. to put him in??? and do you know anything about piranha??? i thought i did but i have this serious algae problem  all water tests i have done (i took a sample of both tanks to petsmart) they all came out ok well i hope you can help thank you ~crystal
ANSWER: Hey Crystal,

First off, there's a BIIIG difference between a pacu and piranha. Pacu are typically not carnivorous. When they are, it's to a mild degree, and generally wont kill fish for meat. Piranha, however, in pairs or groups, can kill cows. Any new fish you add (even if you take one out and put it back) becomes a meal. The best solution to that crisis, is establishing tank dominance by adding your fish together in a specific order.

Befor we get into solving the aggression, your tiger getting picked on needs to heal before you do anything. His bottom lip missing may spell doom for him. Get a plastic tank divider, or borrow a smaller tank for a few weeks and isolate him until he seems to be eating regularly, healing up, and doing better. Petsmart sells fish products with aloe vera, and they seem to help a little in healing. As for the rest, Bag them too when you try to re introduce the oscar. Put him in first, with the others in open bags (so they get fresh air) and hold their bags so they don't escape. After about a half hour, release the one piranha for about fifteen minutes or so. Then the pacu, and lastly the piranha. By doing this, you break up their packs and alpha status. Yes, this may aggravate the balance for a few days and cause need for a new pecking order, but your Oscar will have a shot at regaining top dog status. If he's strong and healthy, he'll keep the piranha in check. If he's weak and just needs his own tank from here out, in two to three days you'll know.

For a side note, oscars, cichlids, as well as barbs, some cats, and other larger fish tend to be mildly to extremely aggressive. Sometimes even cannibals. So bear in mind this is their instinct, and you might have had a happy balance before, but only by a stroke of luck. They may never mix again.

Best wishes, and good luck.

---------- FOLLOW-UP ----------

QUESTION: i have separated my Oscars with a divider and the piranha and pacu are doing great i moved their tank out of the sunlight and much better. Oscar and Angie are doing much better they like being in the same tank just not touching eachother so the divider is working good for now thanks again for solving my problem

Answer
Hey, no problem! Just be careful, oscars typically need larger areas to swim, so dividing your tank will work as a temporary solution. After a few weeks of being in the same tank, and seeing each other, try and let them mix again. The extra room to swim around will be healthier for them, and they may start to get along better once they get acquainted through the divider, so to speak. If things just wont work out with them, then divide them again. But it's always better to try and make their tank space as large, and open as possible before you make any permanent dividing plans.