Low Oxygen

[streetlamp]

Was hoping for some help with a low oxygen problem guys. According to the salifert kit, the oxygen is currently reading between 1-2ppm. They recommend above 7ppm. My tank has not been doing too great and I believe this is to blame.
Here are the specs
33g long - 10g sump
weekly 10% water change (now trying bi-weekly)
Eshopps PSK100 Skimmer (pulls plenty of nice dark smelly skimmate)
4 bulb 48" T5 hellolights retro (was dual 175w MH, recently went to T5)
2 K3's on each end of tank (around 1600gph I believe)
GFO in reactor
Carbon just hanging in bag
Recently started adding half teaspoon of kalk per gallon to top off to help stabilize levels in between water changes and help with night time PH swings

Livestock:
2 clowns
tuxedo urchin
sea hare (helping with some HA)
Zoas
GBTA
Monticap
Leathers
Shrooms
Candy Canes

Tests:
Salinity - 1.025
Ph - 8.0
Ammonia/nitrate/nitrite - 0
Calc is 400
Alk - 8.5
Mag - 1300
Phos - 0.0
Silicate - 0
Copper - 0
Oxygen - 1-2ppm

I tried adding a small airstone but no help currently. Would appreciate any help with raising oxygen levels :thumbsup:

[Randy Holmes-Farley]

I don't believe the kit result in this case. Heavily aerate a cup of water and check it. It should read a lot higher.

[streetlamp]

I don't believe the kit result in this case. Heavily aerate a cup of water and check it. It should read a lot higher.
I just read your article suggesting this, will do.

[streetlamp]

Measured a small amount after being aerated in a cup for ~10 minutes and its significantly higher, around 5 now.

[bertoni]

Hmm, that's strange. I would check the water surface for any signs of an oil slick. I might check the pumps to be sure that they're clean and pumping properly.

I suppose a lot of decay might lower the oxygen level, but that's hard to believe. I might stop feeding for a day or two, to see what happens.

I suspect it's a testing issue, somehow.

[streetlamp]

After letting the water aerate for even longer and testing it, it has significantly risen even more. It is now at 7.

This has been a ongoing problem, the tank has gone around 3-4 days without a feeding over christmas week with no improvement. The surface is heavily agitated, no oil slick possible. It used to have one before I reorientated the powerheads though.

[bertoni]

Well, I have no idea what's happening.

[streetlamp]

Throw a giant air stone in the sump? We are in a small ~500sq/ft apartment with gas everything (heat, stove, water heater). I have been worried too much co2 is in the space.

[bertoni]

If you were aerating the cup of water in the house, the tank should be able to match that same level.

[Randy Holmes-Farley]

Is there a skimmer on the tank?

What time of day did you measure it?

I'd try a tank and aerated cup sample side by side, just to be sure it is not random test error.