Please help, half my corals are dying

Hey y'all I know it's been a while since I've even logged in. I've been busting my arse trying to finish my undergrad AS degrees so I can start studying for the LSATs and start looking at law schools.
ugh.
Anyways, I've had this pretty cluster of zoas for a few months now, and they have just lost practically all color and have not spread yet, as they should be doing. I don't even think 1 new one has popped up.
Also this huge clam which has been very happy up until the past few days, started moving, then unattached it's foot, wasn't as full as it previously was and now it looks as if it's just knocking on death's door.
Duncans haven't been happy in weeks. One's open a bit now but it looks flaccid, and this thing use to eat quarter inches of frozen shrimp and be the size of a silver dollar.
I haven't changed a thing. Done semi-regular water changes and, no I can't tell you what my exact perams are because my kids had a hay day with my test kit. All I have left is the ammonia tester which, there is none and, this tank is established, been up since Nov.
I've been adding calcium and alkaline, no change.

Thing is, I've got jade corals and mushrooms that are doing awesome and so are my fish. One friend suggested I lower my lights closer to the tank but they are only like 6-8 inches from the top.. Coralife aqua lunar lights (T5 with blue LEDs) and another said I was using too much light and should cut back the white hours. Short of taking water to the pet store for testing which, I know I need to to but with school I haven't had the time...can anybody offer me any insight?
I'm afraid this clam's gonna be in the trash by Monday. If not sooner!

40g breeder
.024-25 salinity
74 degrees (SW FL, no heater)

 

Honestly I would say it could be temp. 74, even though it's not unheard of, is very low. Most people run their tanks in the 80 degree range including myself. That clam doesn't look very good though and is most likely gone already. I would bump my temp up a degree or two daily as well as get that water tested. Something is off. l.

 

clam's dead I took the heater out because I had the tank set at 78 with a heater and the duncans were not doing well. I read that duncans prefer cooler temps, around 74. Is that not true?

 

ok so, any insight on the Duncans and the Zoas?

 

74 is def too cold...

How are your nitrates!!?

 

I just ordered a heater online with overnight shipping.
Nitrates 5.0, maybe 4.5

 

Not really enough for algae... Hmmm

Can you discribe the algae? It's is light drown and flat, or more reddish brown and a bit more "bubbly"

 

I don't have an algae problem at all. My glass stays pretty clean, even. I have some brown on the sand bed. When I stared the tank out, I had an explosion of neon green coralline and over time, it's stopped, my dark purple (it was so dark it was almost black) has lessened and now is more pink. I've never ever seen bubbly or stringy red algae.

 

I just put my Duncans on the sand bed in a lower flow lesser light spot and lowered my bleached out zoas too. Also, going to run the actinics all day, and start running the lunar LEDs more and the white T5's a LOT less. I've been running them like 10 hours a day, I'm going to cut down to 6.
I had a heater at 78 degrees and took it out based on some (apparently bad) advice I got about Duncans liking low temps and it got broke. Sadly, I fear the drop in temp is what killed my clam. FML

 

I'm sorry !! I must have mixed up two threads topics here !! Tough to try and be all over the internet at once.