sick Endler fish

Question
Hello David!

My boyfriend and I bought a few fish in July.  We purchased what we thought were a few goldfish; one being a fancy goldfish and the other was listed as some other type, can't remember.  I've been researching fish and found that one of my goldfish is an Endler, cousin to the Guppy.  He is the cutest most lively little guy, we named him Gazpacho and he has been keeping us smiling for months.  Anyways, he's been very ill for the past week.  The fancy, "Gerty" is doing fine, but after some research I find he has been showing signs of constipation.  Gazpacho I believe has Bladder disease.  He has all the symptoms, however this all came on VERY suddenly.  We thought he had injured himself because we caught him in the tube we had hooked to the filter  where the bubbles come out before.  We thought he had done it again and injured himself. He is very either very curious or he was trying to escape. He was fine one day and then laying at the bottom breathing shallow and unable to float up. We have a 1.5 gallon tank which we bought at Wally world the pH is low, 5.5, I added Epsom salts today, raising it to 6.0. My boyfriend just went and payed freakin' 8 bucks on pH plus which I saw you said it is just baking soda.  We set aside water treated with the pH plus, as back up for the water change tomorrow.  We have Gerty the goldfish in a separate bowl to keep his ammonia away.  I have read to feed Gazpacho a pea, but I seriously doubt he will eat it. A few days ago was the last time he even attempted to eat and he held the food in his mouth for about a minute and then spit it out.  His breathing is very labored and he isn't even trying to get to the top to gulp air like he was a few days ago.  Is it too late for him?  I have read about antibiotics, but have no idea what to look for and I don't want to change his environment too much at one time.  I have been doing partial water changes very regularly, but did not separate the 2 fish until today.  Also, we purchased a charcoal filter and have that going even though he seems too weak to fight the current it creates.  I have the filter blocked with smooth glass stones to keep him from getting trapped.  Please let me know what to do, I don't want to do too much and kill him, but still want to take as much action as necessary.  Thank you!

Answer
Hi heather...  If he is not eating... then I would try to feed him some brine shrimp to see if that will stimulate his appetite... Is this a guppy??? or a goldfish???? I would just do a water change with him to make sure it is not a toxic tank and then I would add some aquarium salt.  The pH is way too low... but you have to adjust it slowly or you will shock him to death.  I would try about .10 of a lb of coral sand in the bottom of your tank... I would also try to get your tap water tested too.... keep me posted please... dave