ORP or O2 test which one????

[prow]

hey everyone. i started to stock my tank recently and had a ittle issue. well here is the set up.

115ish gal 72X18X20 tank with 1/2" sandbed and 140lbs live rock.
45gal sump with mud and caulerpa. lighted with 3-18watt T5's
10gal sump with ASM G-3 skimmer
flow:
sedra 1200gph return pump.(one pump for both sumps)
tunze stream 6000 with controller(alternates at 1850gph and 1500gph)
3 maxijet 900 powerheads on wavemaker.
lighting in maintank is 6 80watt T5's.

the tank has been going for a year. after stocking some wrasse's they lasted about 3-4months. i noticed them breathing heavy the night before they died and thought either gill fluke/ich or low O2. thinking more on the low O2 because there gills were blue after death. so the tank has been sitting with only the cleanning crew, shrimps and snails (lots of pods and mysids all over too) for the past 40days. i have new fish ready to go in, been in the hospital/isolation tank for about 40days now. bought them right before i had issues. before i put them in the main tank i want to make sure its ready so i bought a salifert test kit for O2, the test kit sucks. i cannt read it, i get a different color than the color chart/card. so i am thinking i should buy a pinpoint O2 monitor or ORP moniter. so which one should i get? i do understand what the ORP tests. just not sure if i should get it or the O2 monitor. the ORP monitor is about half the price, but if the O2 would be better for my needs i dont mind spending the extra cost to get the right monitor for me.

the rest of the tank levels:
Temp:80
Ca:420
ALk:2.97
ph:8.2
salinity:34
NH3/NH4:0.0
NO2:0.0
NO3:0.0
phos:0.0
silicate:0.0
O2:can not read this stupid test.

[BubbaWPB]

ORP is only good as a relative test (i.e. watching for changes) and measures the amount of electrons available for oxidation reduction reactions. Yes, oxygen is a good electron donor, but other substances are also good electron donors and will also show high ORP. Sulfuric acid shows high ORP levels, for example. So a high ORP level does not ensure enough oxygen in solution.

If you are worried about your oxygen level, make sure your tank has good circulation and is open to air exchange. Many other things can cause hypoxia (low oxygen levels) in animals other than the lack of oxygen in the water. Gill parasites, for example, can prevent oxygen from being absorbed by the fish, which can result in a purple or blue coloration to the blood and gills.

Your gas exchange - including oxygen - should be just fine. (Since your alkalinity and pH are normal, there is adequate exchange of CO2, so O2 exchange should also be good.)

Unless you are doing scientific research, the O2 monitor is probably a waste of money (as is the O2 test). ORP is useful if you run an ozonizer - it makes sure you add enough to work without poisoning your tank. If you don't have an ozonizer, the ORP probe is also pretty useless.

Bottom line: your oxygen level is probably just fine (given your other tank readings). Your fish probably died of an illness that caused it not to be able to absorb enough oxygen (gill parasites).

[prow]

hi thank for the reply. i hope that it is just a parasite, so much easier to deal with. the O2 readings seem to be going up, at least on this kit, its hard to read. think your right though no real need to buy either monitor. i do have a canopy, thinking of rasing the lid so there is a 1-2" gap, allowing for the air to move a little easier. the tank is acrylic so the water surface is not fully open to air. hope i said that right. could just be the tank is to sealed up and the lack of air movement in the room not enough gas exchange, but yeah my ph is pretty stable so i could be just a parasite. lol, i was just thinking how often do we hope for a parasite. now i find my self hoping i do have a parastie issue.

[BubbaWPB]

I'd definitely make sure there was some way for air to get to the top of the tank. ...and your refugium will help a lot to stabilize 02 levels, too. Since you're growing caulerpa, I'd suggest running the lights on the refugium 24/7. It allegedly helps prevent them from going sexual, and also puts out O2 24/7 that way.