I need help with a new tank?

I have had a 26 gallon tropical community tank for almost a month now. for the first three weeks everything except the ammonia, nitrate,and nitrite levels were fine. the ammonia and such were fluctuating from stressful to harmful levels so i added aquarium salt, and did the water changes as i shouldve. however after three weeks i purchased a ten gallon tank to use as a nursery for the babys the females were having. i used the water from the 26 gallon and then filled the 10 gallon. after i decided to do a gravel cleaning due to the ever present high ammonia levels. well after the gravel cleaning the water got really murky, a grayish white cloud. it hasn't changed for over a week. in frustration with the water color i did a 50% change about 3 days ago. the water hasnt changed at all. however now the PH has gone down to around 6.2 or lower and i lost a snail to that drastic decrease. the plants in the tank are dying and it appears that the fish are getting affected now also. theres about 10 fish total including 2 silver tipped sharks who seem to be getting fin rot, or at least a discoloration in the fins, and look like they just might be dying. i don't want to move them into the nursery since i have it full of baby guppies and don't want to lose the babies. how can i fix it? ivee used PH up, aquarium salt, raised the temperature, added a bacteria supplement, changed the feeding from flakes in the morning, bloodworms at nite, to just bloodworms in the morning and now to every other day and stil nothing has happened and it appears to be getting worse. i need to know what might be going on. its a little unnerving not being able to help these fish. i have the temperaturre at 80 degrees, and tthe 10 gallon tank is perfectly fine which i also find bizzare since both tanks shared water. the 26 gallon also has a slight fishy stench to it that the 10 gallon doesnt. someone please help. ive read all that i can and nothing has helped so far.