blisters on my fish

Question
QUESTION: I have 4 large oscars that came with the 240 gallon tank that I bought.  They have been really healthy but this morning my son noticed what appears to be blisters starting on the top of two of the fishes heads.  They are not tall blisters but they are dime size a look like a blister.  One of the fish has more than the other.  The are a mated pair so do not know if that is why they have them and the other mated pair does not.  I know my husband did about a 4-5 inch water change the other day as our water was turning yellow.  He treated the water before he put it back in and he used luke warm water from the kitchen.  That is really the only change there has been.  This paticular set spawned about a week ago but they ate the fry.  Do not know if that makes a difference.  There is four oscars and 1 arawana in the 240 gallon tank.  No live plants and I have two bubble wands running all the time.  Please help!

ANSWER: Ok are the blister like indentations or are they like a bubble? IS your tank filtered? if not you need to get filters and is it heated? if not you need to get a heater. With oscars you need to do weekly water changes of about 15% of the water with a gravel vac and with the vac be sure to stick it in the gravel. The things you are describing to me sound like hole-in-the-head it is mostly caused by an unhealthy and low protein diet. To fix the cloudy water use "Jungles cloud clear" and if your fish has hole in the head use "general cure" and aquarium salt.

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QUESTION: The look like blisters but they are not raised.  No holes though.  We have a really great filtration system and the tank is heated.  The water has not been cloudy at all it just had a yellowish tint to it.  We did the water change about three days ago and it cleared right up.  We use a gravel vac and really give it a good cleaning.  As for food they are on a good quality cichlid pellet that I was told was one of the best.  Now we do not do the weekly water change but since it was just changed you would think the quality would be pretty good?  So what do you think?

Answer
I have never heard of what you are telling me before see if their is any changes in the next few days, and report back to me. Also have you checked ammonia, nitrate, nitrite, P.h., alkalinity, and hardness if not i would start to make sure every thing is balanced and where it should be. To have good water quality you need to do regular water changes at least once a week with replaceing about 15% of the water. Also along with the food feed them frozen blood worms and frozen beefheart then they will have a perfect diet.