I'm fairly new to plants (~6 months) and still getting a bit of a handle on ferts. I started noticing my sword (gone now, outgrew the tank) had 'the twisties' and my Hygrophila had quite a few cupped (edges folded in) leaves. This, combined with my ramshorns' shells becoming white and pitted, led me to belive there may be a Ca deficiency going on here.
I've just had a look at the water report, our tap water contains ~35ppm Ca. I added a teaspoon of CaNO3 to my 500ml fert mix when I made up a new batch last week, so it's a little early to tell if it's enough, but I was advised to start slow and not add too much at once. I'm considering buying a test kit, but since they're generally designed for SW I'm not sure if it would be accurate - I did a search on the forum and found a few related posts but no definitive answer.
My question is how many ppm of Ca should I be aiming for? Is a kit worth it, or should I continue to use the plants/snails as a guide?
For reference, here's my fert mix:
1/2 tsp KH2PO4
1 tsp CaNO
2 tsp KCl
2 tsp MgSO4
3 tsp Mg(NO3)2
6 tsp T.E.
7 tsp KNO3
500ml tap water
The tank is heavily planted. I add ~6ml/day to this tank to maintain 5-10ppm NO3, and use Fleet if I need to up the PO4 to keep a 10:1 ratio.
65g test results (taken tonight):
KH - 50ppm/3* (it's ~70ppm/4.5* out of the tap)
pH - tank w/ CO2 - 6.4 (tap after sitting 24h is ~7.4)
GH - 140 (ppm CaCO3)
If more info is needed, detailed tank specs are on Aquaria Central, there's a link in my signature