Invert Die Off, Please Help me

[waterbury guy]

My tank set up is in my sig established Jan. '02. In the last 30-45 days I have lost two cleaner shrimp, one fire shrimp, 2 fighting conch, 10 scarlet hermits, and I see no more amphipods after lights out. Only inverts left are two feather dusters, red serpent star, bumble bee snails, and some bristle worms. All these appear to be fine. All fish seem to be doing fine as well, except my fire goby seems to hide much more than previously. Here are my test results from today:
Temp: 80
SG: 1.24
PH: 8.1
ALK: 5
Ammonia: 0
Nitrate: less than 10
Nitrite: 0
CA: 380
I feed about 5 times a week a mixture of fresh fish, prime reef, mysis, brine, blood worms. Dose w/ DT's every other day.
Here's what I've done differently in the past 60 days:
1. Was doing 10 gallon H2O changes every 10-14 days, now 5 gallons every 14-21 days and just top off with fresh RO of 1 gallon per week.
2. Installed a third powerhead (MJ1200) on a timer, turns off at night.
3. My 50/50 40W NO bulb burned out, replaced w/ a reg. NO 40W.
4. Stopped dosing tank w/ SeaChem Reef Builder (was doing about 1-2 times a week.)
5. Started dosing w/ SeaChem Marine Buffer three times a week, or put a teaspoon in my 1 gal. RO fresh water. PH was always at 7.8-8.0, now 8.1-8.2 (8.3 when I first put it in). I think this has raised my ALK as well as it was never as high as 5.
I have never tested for copper, magnesium, or phosphate. Also I have never run a skimmer, sump, or refugium. I am planning on adding skimmer very soon. Any help would be really appreciated.

 

[bang guy]

Is your ALK reading Meq/L or dKH?
I fear it is Meq/L. If so then I believe your invery problem is from PH fluctuations. The inverts you listed do not handle wide fluctuations in PH very well.
Adding ALK without balancing Ca can cause precipitation. When the Calcium carbonate precipitates the PH falls very quickly and then slowly climbs back up. You need to find your PH range as it varies throughout the day. Test early morning and late night, that should be pretty close to your actual PH range.
If you ALK is listed in dKH then my theory is useless

 

[waterbury guy]

You are correct, it is Meg/L. Before I started dosing with Reef Buffer it was around 3.5 or less. Should I stop using the Reef Buffer? If so should I add anything to the fresh RO top off H2O?

 

[bang guy]

The Buffer product is fine but it must be balanced out with Calcium and in much smaller doses. By now I would guess that your Magnesium is depleted or at least low. I don't see any heavy Ca users in your list. I think my initial recomendation is a couple good water changes. You don't need any additives that I can think of, just regular water changes.