Its... complicated

[Neuve]

Hello, all: it's been a while since my last post, cause I've been away for a very long while.

Long story made short: My brother gave me his old (and pseudo alive) SW mini tank as a gift for Christmas, so I was caught with this surprise I did want but not right now, but anyways, I'm willing to go all the way just because I love the fish.

Anyways, because of the setup, I was going a bit crazy:

The Setup

2 gal tank (IQ3 Dymax) It comes with a filter attached to the back.
1 large piece of 'live rock' (with what my brother described as a pair of 'sea cucumbers but in a very small way. The one i can see actually looks something like a furry worm displaying something like red tentacles on one end. It doesn't move from place). Also, the live rock seems to be growing some very little hairs, and
2 pieces of dead coral for decoration
1" crushed coral sand bed (when the tank arrived it had some little white bugs, apparently 'pods', on the tank, now they're harder to spot)

It had a non-regulable thermostate, (but i bought one today, specifically made for this tank), I also bought a small protein skimmer thinking of reducing biostress and helping a little to aerate water.

The (other than LR-attached) live stuff
2" Basslet Diadema Fish
1 small hermit crab (similar in size to this one)

The stats:
Today I also bought a basic kit for testing water, but it turned out that the mini master from nutrafin only tests for ammonia in FW, so I cannot check for that now.

Nitrites - 0.3 mg/L
Nitrates - 7 mg/L
pH - 7.2
Temp - 80°F
Specific Gravity 1.022

The questions:
Is it possible to keep the crab and fish alive and weel in this environment? My brother had all of these running for one year, but he decided to get a bigger tank. There is nothing i can do for his fish or tank, but for mine...

How can I do water changes? I bought some instant ocean, and my brother gave me 1 gal of RO water he bought from the aquarium.

What do you suggest, besides getting a bigger tank?

All help is appreciated. I'll post pictures in the morning.
TIA

 

[Neuve]

... Also I bought some AC to replace the one in the filter, because my brother didn't change it, ever.

Temperature's been @ 81°F since i changed the thermostate.

 

[Neuve]

Update 01-01

Here are the pictures:

In the first one you can see Ray, my fish. On the background, in between the dead coral and the LR there's Pedro, the crab (gray spot). He changed skin and stayed there for more than two days, until I thought he was dead (he shed his colored skin, so I thought the worst) so I moved him, a bit and then there were two Pedros, one dead and one alive, and now he's kind of eating his own remains . I hope that makes him happy. Should i get him a bigger shell?

Here is a picture of him before shedding. He's been very shy ever since (before that, he was climbing as high as he could, and showing off his bright orange colors).

And lastly, what my brother said to be a sea cucumber, which has been very shy also since I rearranged the LR

Whenever it comes into the open showing off his tentacles i'll take a picture.

I have spotted a pair of white dots moving around. If this was a FW tank, i'd say i've got some snails. Pretty small though, they just move slowly around the glass.
Should I worry? I don't care about having a snail, but I wouldn't ever like to treat with copper.

Stats:
pH was 7.2
Temperature, steady at 81 F
Nitrates were 7, now, they are below the scale.
Nitrites were 0.3, and still are. When adding the new AC I did a PWC. The old AC is still there, and also, I guess somehow the protein skimmer is working, even though i'm not getting the gooey slimey stuff i've seen at some aquariums.

All thoughts appreciated.

 

[Neuve]

Ok so one of the cucumbers has decided to come out and play: here is a pic.



There is another one with long red tentacles, but he's still hiding.

 

[Neuve]

Did a PWC yesterday.

Tested afterwards, and Nitrates are spiking, which could mean that some more bacteria have established, since I am getting nitrogen at the end of the cycle. Tested RODI water and levels are 0, so whatever nitrates I'm having must come from the tank. Will feed a little bit less, and will do another PWC tomorrow.

Also, my pH is around 7.5, so I'm guessing I should do something about it? Fish, crab and cucumber all seem fine.

 

[Beengirl]

I would add some Kent's buffer to get the pH up.

 

[danbstrong]

Did a PWC yesterday.

Tested afterwards, and Nitrates are spiking, which could mean that some more bacteria have established, since I am getting nitrogen at the end of the cycle. Tested RODI water and levels are 0, so whatever nitrates I'm having must come from the tank. Will feed a little bit less, and will do another PWC tomorrow.

Also, my pH is around 7.5, so I'm guessing I should do something about it? Fish, crab and cucumber all seem fine.

Tank Looks good ph is low tho might wanna check alk cal and mag as well

 

[Neuve]

Thanks for the advice, danbstrong and Beengirl! Will do and keep you updated!