Need advices on dKH, Ca and Mg

[clownfish_forever]

Hi brothers,

Need some advices on this topic. My 120 gal aquarium is made up of 60% softie, shrooms and zoas, 30% LPS and 10% SPS - in fact I only have 1 monti and 1 acro.

Before I keep SPS, my parameters are:

dkh:7, ca: 500, mg: 1280

Ever since I keep the SPS, I noticed my dkh and ca starts to drop. Since I only have 2 SPS corals, I started to dose Brightwell Alkalin 8.3 (20ml) and PurpleUp (20ml) twice a week. I began to observe good PE and sign of growth of the SPS and coraline algae. Now the questions are:

1) Despite the dosage, my dKH still remains around 7. Does that mean I should dose Brightwell Alkalin 8.3 more frequently to up the dKH? my ca is now around 400 - 420. mg is still 1280.

2) I understand SPS use the calcium and bicarbonate to grow, if my tank has low dKH and Ca, does that mean my SPS will suffer? or they can still be happy just that wont grow?

3) Is that a cheaper source for dKH? I have read about limewater and baking soda...but I also heard about the cons, for instance baking soda will slightly lower the pH.

Since I do not intend to go full-scale to SPS, I really wonder if I need to be so concious of the dKH and Ca of my aquarium.

4) I have one frag of monti that has half of it become white and died off already...I think because it dropped onto a yuma then become like that...just curious whether those died off part of SPS can recover? or I should simply break off those died-off part?

Thank you. Any view and advice is welcomed

[kraken]

for alk, you can dose food grade sodium bicarbonate (cheaply available), it has little effect on pH, however, if you dose sodium carbonate, it will increase pH.

dKH = 7 is still manageable, however if it is slightly higher would be more ideal.

CA try to maintain about 430 - 450, same thing, you can find food grade calcium carbonate cheaply

for your monti, do the white parts still show polyps? if not, its a goner, better to frag it away

[clownfish_forever]

Thanks for advice. The white part of the monti is beginning to show the colors...I am hoping that it is recovering.