Concerned About Yoyo Loach

[CKutz]

I've been concerned about my yoyo loach for awhile now...nothing seems immediately wrong so I didn't make a fuss about it, but now it still hasn't changed much.

I bought 5 yoyo's a few months ago. 1 died the next day. of the 4 remaining, two have grown to almost 3", they are active, always feeding, and swimming around. A third one, is about 1/2 an inch smaller than the other two, but it is pretty active. the 4th one is the one i'm concerned about.

the 4th has barely grown since i got them, maybe 1/2" in all this time. He's also very often on his own, and inactive. This has been going on for quite some time, and i can't figure out why it is.
people say that yoyos usually grow really fast at first, so its odd that he hasn't. also how he doesn't go for food as eagerly as the others. I feed them shrimp pellets, algae wafers, and occasionally frozen food and frozen brine shrimp (also flakes, but i don't think they eat them, just the other fish).

my tank is 30 gals. it was cycled, everything was fine for a few months. then my filter broke, and i ran two backup 10 gal filters till i could get the part for the filter. i guess because of that whole thing my tank has gone back into a cycle. but this behavior has been going on for quite awhile, and the other loaches haven't acted this way. the ph is low somewhere from 6.4-6.8 but like i said the other loaches have been ok.

any ideas?
thanks!

 

[WILDER]

Does he look thin or bloated.
Does he have a sunken in belly.
What does it look like when he goes to the toilet.
Does he look pale or darker in colour.
Does his eyes look sunken in.
Does he act listless and lethagic.
Does he lay to one side, or rest on things in the tank.
What temp is the tank.

 

[CKutz]

-my other yoyo's eat till their stomaches look like they will explode, and i never saw his like this, but i wouldnt' describe it as being sunken in, but slimmer than the others
-he was typically more pale than the others
-never noticed the eyes
-yes listless and lethargic...i've seen him laying on the bottom before and almost completely roll over
-yes he's typically laying on the leaves of the one decoration, meanwhile all the others are swimming all around looking for food like they do.
-temp is 76-77

this was on my mind to post for quite awhile so i did..but now i've finally had a chance to sit around and watch the tank for awhile today. he is much more active than usual. his colors are more bold now also. tested the tanks stats and the ph has risen (i added a small bit of what i think is live rock, it came with the tank which was used and when i had the whole thing in before the ph was up around 8, took it out and it dropped to 7. so i added a little to the filter to try and raise my ph again to help with cycle). the ph is probably around 7 now, 6.6-7 for sure.

kinda skeptical that it's just the ph though because the other fish were still much more active, they were all purchased at the same time and were almost the same size. so while the stats were good on the tank, he should have grown just as much i would think?

yet he's been like this for quite awhile and hasn't died or gotten worse

 

[WILDER]

You need to remove the rock if its altering ph.

Being pale, listless and lethagic and rolling over can be signs of ph shock or a bacterial infection.