Corals dying?

Okay, here goes nothing, I'm so new to this and I ask that you be kind because I'm frustrated and confused.
I read somewhere that everyone needs to know absolutely everything about the tank and the way I'm running it, so I'll try my best.
So, about 2 weeks ago now I noticed my torch coral in my 55L (14.53 gallon) nano reef wasn't fully extending and was concerned, I tested my levels (by levels I mean nitrate, nitrite and ammonia, rookie move that after 8 months of having the tank up and running I had no idea about KH, magnesium and calcium. will go further into detail about that later.)
Levels all came back fine, except nitrate which always tested as 4mg/l (it's a colombo test kit that I got the same day we set up the tank.) and could not seem to bring down the levels no matter the amount of water changes I did (little did I know about no pox.)
So anyway, I make my way to my local fish store armed with photos and a million questions, only to be met with the inevitable question about my calcium and magnesium levels. We already knew our KH. However, after a million times I also explain our nitrate problem, I told the lady the test kit I used, she was confused and said she had never heard of colombo, sold us a red sea nitrate test kit, and a no pox after we had tested the levels.
The same day we went back with a bottle of our tank water for the calcium and magnesium levels to be tested and the results were as follows, including my normal tests from today.
Ammonia: 0.25mg
Nitrite: 0.25 if not less
Both of those done with colombo test kits.
Nitrate: somewhere between 0.25-0.50, which shocked me because my colombo kit ALWAYS showed it as 4mg/l, which begs me to ask the question as to whether or not my colombo test kits are reliable. Have checked the usage date on all of them and they are all in date.
KH: 8.4
MG: 13.60
Cal :4.30
Salinity: 1:025
We are also picking up the supplements and tests for the calcium and magnesium this coming Saturday.
So here's my problem.. They said my torch could be in the state it's in because of the calcium levels, however, although it is opening now, my goniopora seems to be struggling now.
I was inspecting my tank this morning and also noticed maybe a penny-sized insect in there, and then when it ran out, had some sort of fluffy tail. I have no idea what this creature is and I also apologise for how long this thread is, and I am nowhere near done explaining.
I'm also having a huge green hair algae problem, along with the fact that I've seen a huge bristle worm in the tank that I can't seem to get out.
Sorry, I'm all over the shop, let me get to the important part.
It's a 55L (14.53 gallon) nano reef. I run the Fluval U2 with biomax, biofoam, polycarb and aquamanta's PhosNitra Reducer and 3 huge pieces of live rock (Idk the weight.) One of (I'm not sure which) the Fluval sea wave makers.
So livestock wise, I have a torch coral, a goniopora, what I think are star polyps, and a pulsing xenia, and an ocellaris clownfish pair.
I'm sure I'm supposed to tell my phosphate level, but I don't have a kit for that.
Also I've had a huge spike of diatoms recently and some pinky/red spots on my live rock.
I'm also confused about the 'don't touch your sandbed rule' however, have read that other people say it's a myth.
I'm not running a skimmer or anything, questions are welcome, and please look at the photos below so you can understand what's going on.

 

If Red Sea is showing Ammonia and Nitrite then that is your first issue. A cycled tank should be zero for those. In addition, Torches prefer dirtier water for nitrates (ie 20ppm). Torch corals are among the more sensitive corals.

 

If Red Sea is showing Ammonia and Nitrite then that is your first issue. A cycled tank should be zero for those. In addition, Torches prefer dirtier water for nitrates (ie 20ppm). Torch corals are among the more sensitive corals.

My test kit for ammonia and nitrite is not Red Sea, it’s Colombo

 

HI there, sorry you're having so many issues at once, it can definitely be daunting especially when you're new to this! As Jesterrace has noted, any trace of ammonia and nitrite can upset things but also generally speaking any sort of parameter swing or change can also present issues. Its important to know your phosphate levels though so I'd advise having your store test for that if they're able. Its worth it however to grab a test kit for it if you're able so you can test whenever you want! You also don't want it to read zero, generally mine is between .05 and .03.

Algae can sometimes be caused by high PO4 (phosphate) but also, a CUC (clean up crew) is important to have in a ny reef tank as they can help keep algae and detritus in check. These can include various snails and crabs, depending on what you need. I have in my tank, a handful of hermit crabs, emerald crabs, trochus and astrea snails. Using RODI water to mix your salt is also important since tap can contain all sorts of nasties that can contribute to algae and poor water quality in general.

To get your corals happy and thriving again, its most important to keep your levels stable as I mentioned earlier. This can be managed with small weekly water changes for now but as your reef grows, you may want to look into dosing alk and calcium regularly. This is where testing kits are most useful, so you can figure out your consumption rate and dose accordingly. If all that sounds too manual, auto dosers are available and can be set to dispense a set amount at a designated time regularly so you're not having to worry about it so much.

Hope this helps somewhat, and best of luck! Reef keeping is stressful at times but so worth it.. in my opinion

 

Is your calcium level really 4.30 or is it 430? If it’s 430 that’s completely normal.

Are you using RO/DI water or tap water? If tap water that could be some of your issues with algae growth and what not. If using tap water your levels of concern mentioned above maybe coming from your water source.

Are your clowns trying to live in and irritating your torch coral?
If you have a reef tank you really should have a skimmer. Your tank is small enough to get away without one but what’s your water change schedule?

How’s your light level and your water flow
What filter are you using?
I’ve never seen a bug like that when in doubt throw it out.
How’s your feeding? And fresh water rips offs? Evaporation/salt level and temp swings can prove deadly fast for corals.
The red dots are a type of coral one algae and nothing to worry about.
Never heard of those test kits. I’d get some salifert ones.
Also mentioned hair algae issues but I don’t see any in the pictures provided.
Agree with what was said above.