OTOs say: something is wrong!

Hello All,

I have a 30g tank like that:
- PH 7.5
- temp 26C
- 4 otos
- 3 SAEs
- 2 guppy fry
- lightly planted

everybody was happy!

last month I got 4 rummy noses; lost 3 of them during the 19 day QT
period; no illness: 2 due to PH shock and 1 jumper;

the only survivor rummy was rather sad alone; so I got 5 more rummys; on
day 5 of the QT period I thought to myself:
- they come from the same tank from the same shop;
- they look very healthy
- the PH of the QT tank is already 7.3 (was 6.5);

so yesterday I put them in the main tank;
after some 30 minutes they were swimming around rather relaxed;

today I did a light gravel-vac and a 10% W/C;

after that the 4 otos started acting *very* stressed! they swimm around
the tank in an erratic manner; they do very fast figure-eight patterns
against the glass.. usually they hide during most of the day;

temp, PH, NH3 and NO2 are fine!

everybody else (SAEs, guppies and rummys) is fine!

I'm doing a 30% W/C right now and the OTOs seem a bit (just a bit) less
stressed;

what could be bothering them?
I'm afraid of parasites (tho they are *not* flashing)

TIA!

--
Otavio Exel /\oo/\