Hi all,
I have a tank that can take up about 650 L of water. I used 7 bags of AS and that consumed 9L (volume of each bag of AS) x 7 = 63L. The rocks and driftwood took roughly another 10L the most.

So I am left with about 650 - 63 - 10 = 577 Liters of water in my tank.

I could work out the other EI components (NPK) but am kinda lost with the amount of Calcium and Magnesium that I should dose for that much of water. I have Calcium Sulphate (Plaster of Paris) and my Magnesium source is Epsom salt.

I would appreciate if someone could let me know how many teaspoons of Calcium Sulphate and Epsom salt that I should add after every 50% WC. Thank you in advance.

Question is, what's the Ca and Mg of the tap water?

Then you can figure, plants will not use much more than 10ppm of Ca and 3-5 ppm of Mg I'd imagine per week under extreme high rates of growth.

I generally suggest with most GH's, to add another 1-2 degrees of GH booster to the routine after the water change.

Regards,
Tom Barr

Unfortunately the water company here is uncooperative to give that sort of detail. But we have soft water here with GH around 1.5

If I am targeting, say, 6ppm Ca and 1.5ppm Mg, what would be the amount in teaspoons would that be. Yes, I have only measuring spoons but not gramme scale

On top of that, Tom, is 6ppm Ca with 1.5ppm Mg an acceptable concentration. If okay, then I will increase it bit by bit when growth becomes better.

I wish we have that available locally

Gh booster is legal in all 50 states, Canada, and mexico

Cheap too.

Add about 1:2 parts MgSOI4/CaSO4, you can us ea dosing cal to get precise measures, but 1/2 teaspoon per 80 liters should be more than enough, remember that they have 2 H2O's and 7 H2O's(Hydrated salts).

Yes, 6 and 1.5 ought to fine 2x a week.
There are no bad effects, only good ones as you add more than say 1-2 GH's to the water, up to at least 7-10 range, you get better colors.

Regards,
Tom Barr

Tom, I am in Hong Kong. Sometimes I fly to Malaysia.

Thanks for the advice.

Here's a related question: If my tap water has 20ppm Ca and 1.6ppm Magnesium on average, do I need to dose GH booster?

I've got a 20gallon with fluorite substrate, pressurized CO2 (keeps my drop checker a steady green) and 130 W of light over it. Plants are growing great. So's the algae *sigh*. I'm struggling with green dust algae and the dreaded clado. I'm guessing it's from fluctuating nutrient levels - I haven't been doing proper EI dosing. I've just been throwing the ferts in once per week, after the water change. I'm beyond tired of testing the water, so I'm thinking I'll adopt the EI method, and just dose every other day and do that big water change once per week.

I'm rambling...

Anyhow, is that enough Ca and Mg? If it's not enough of the latter (which I suspect), can the plants pull the Ca from the tap water, and I can top up the Mg with epsom salts?

Other stats on the tank:
pH is around 7.3
using a Magnum HOT filter (love it!) rated 350gph flow. I've slowed it down a bit by putting a sponge over the intake
substrate is fluorite as mentioned, mixed with geosystems gravel (same shape and color, just a sort of inert clay gravel)
hardscape is some natural river wood and river rock (which I boiled the heck out of!) from the Fraser River.
Tank temp is room temperature, about 74F
CO2 is running 24/7 at about 2bps (drop checker is green to yellow-green)
plants are a bit of this and that: ludwiga, rotala, cabomba, some crypts (including parva), some vals, hairgrass, a nice red plant who's name I forget, and some odd and end stems I pulled out of my 90 when I switched it to low light
fauna is a pair of GBR, a bunch of platies, some cherry barbs, panda cories, couple of otos, a bamboo shrimp, a handful of tiger shrimp and 8 amanos.

If you cut the light on that 20 gallon tank from 130 watts to 65 watts - remove one bulb - your algae problems will be a lot easier to solve. If you raise the light fixture a few inches above the tank, it gets easier still. You really have far too much light now. Then switching to the EI method will do a lot of good, as would making sure you have good water circulation all over the tank - all of the leaves should be in motion.

the lights are mounted about 7" above the water's surface (it's an open top, rimless tank). And the tank is more like 22G (it's a funny size), not that it matters much. 6.5 wpg is high light, I know, but I didn't think it was too high? If I drop it down to 65W, that's just 3wpg, which is only medium light I thought? The tank doesn't look unnaturally bright - it looks quite nice, IMO. Except that I'm having to wipe down the glass every couple of days.

IMO, 65 watts over a tank that size should be able to grow about anything quite well. Mind your CO2, ferts and water changes and it'll grow in just as good as it would with twice the lighting.

I should've clarified - I've only got the full wattage on for a 3 hour burst. For the remaining 5 hours of my 8 hour photo period, it's only 65W.