EDGE

First off, Welcome to the board

I am using a 20 oynx / 80 flourite mix in the tank. The plants are rooting really well and the buffering of oynx is working.

The only problem is gH. Is it normal for oynx to release only Mg as a source of gH into the water?

After water change and before the next water change, I test Ca level in the water . It remains stable while gH raises. gH raises by 1 every 3 days.

Tap water is 0 gH and 0 kH.

I am getting signs of Ca deficiency. The other nutrients have been sitting at desireable level.

pH is 6.5
kH is 2 to 3
gH is 2 to 4 with oynx alone

gH is 4 to 5 when I dose Calcium by 1/4 tsp.

Thanks for your help

Seachem

Given the breakdown of Onyx as below it would be hard to see magnesium rising without calcium rising within remotely the same ratio. Calcium is in Onyx at almost a 2:1 ratio vs. magnesium.

Concentration of nutrients in Onyx Sand™
Aluminum 822
Barium 5
Calcium 197500
Cobalt 4
Chromium 10
copper 4
Iron 2846
Potassium 417
Magnseium 115400
Manganese 43
Sodium 135
Nickel 7
Vanadium 8
Zinc 23
Units=mg/kg, source: Plasma Emission Spectrometer, EPA Method 3050, Univ. of Georgia Chemical Analysis Lab

I am curious on a couple of points you mentioned.

What test kit are you using to measure Ca? Most of the tests for calcium are made for saltwater and would not read too well in freshwater. If your calcium reading is off, perhaps the signs of calcium deficiency are actually signs of an over-abundance of calcium.

Also, what form of calcium are you using to dose calcium?

EDGE

I am using Hagen Ca test kit.

I thought the kit was not working properly as well. I email Hagen and they said in parts of BC, I will not get a reading because of the very soft water. When I test with the addition of Turbo Calcium, it does detect Ca in the water.

Throughout the last 1 1/2 year, I have move from dolomite, to crushed corals, to oynx, and most recentl Turbo Calcium.

I have only started higher level of Turbo Cal in the last week. I am giving it a few weeks before making any conclusion on the addition of Turbo Cal in the tank.

I was having very bad leaves crunching up when it was just oynx.

Seachem

You may or may not be aware that you are then adding Calcium Chloride. Chloride is quite unhealthly for plants. I don't think it is the cause of your leaves "crunching" given the timing you mentioned but nonetheless it does have the potential of being a bit hazardous long term. You might consider playing with our Reef Calcium instead. It is a polygluconate calcium which would provide only beneficial compounds secondary to the Ca.

Also, if the kit is not giving you accurate readings and it is detecting some calcium in the water when you add Turbo Ca you do not know to what level this is legitemately taking the Ca. In fact, the kit may be picking up only high levels? So there may be Ca in the water but the kit may show zero. You might double check with Hagen on that but it would be possible I should think given a demonstrated rise in GH daily and the nature of Onyx. Perhaps Hagen might have a means of adjustment for Ca reading in freshwater.