I) So RO/DI water is preferable for the job, right? If I need to use tap water, how to treat the water? Any thoughts on that? Also, RO/DI water is very low ph. In that case, how to maintain high ph of sea water?
Ans: You will need to dose either 2 PART Dosing or have to do commercial dosing. That will buffer up the ph also, aragonite sand will act as a buffering agent, so nothing to worry about that. We have many commercial phosphate removers. So, unless your water is very hard, plain aerating will do.
II) I am planning to get Reef Octopus 150INT skimmer. It should be fine? It is according to BRS suitable for 150 gallons. Mine should be less than 120 gallons including sump.
Ans: Your water volume will be big as you have a big sump. I dont think that will cause any problem too. If you kept the bioload less, plain partial water change after a regular gap would have sufficed and you could have saved a lot there.
III) For the refugium part, to grow micro algae and pods, we need some nitrate and phosphates, right? In that case, using phosphate, nitrate removers are needed or not?
Ans: Thats tricky. You will grow these macro algae so that they can consume the N radicals from the water. But if you use these chemical stuffs, you might end up starving them.
IV) I wish to have three chambers in sump. Water from tank directly comes to skimmer part, then goes to return pump section (middle part), from return pipe, one line goes to refugium. Is the design ok? I think in this case there is less chance of the pods being skimmed out.
Also, any more chambers needed in the sump?
Ans: That will also cause most of the dirt and other "stuffs" in the skimmer and this can damage the skimmer. If there is no prefilter, then it would damage your skimmer beyond recovery. Once your tank matures, you will find stuffs everywhere. I have snails in my sump as well as some sponge colony. they passed the sponge mechanical filtration and then went inside the second chamber. In my first chamber, i find bristle worms with size over 4" every time i clean them. So, water inside the skimmer should always go through the first chamber of physical filtration.
V) I have read in most of the forums that DSB can be disastrous in long run if not proper care is taken. Also, it is not recommended for beginners. Hence, I will go for shallow depth substrate. Now, which one to use? Aragonite/crushed coral/Live sand all are there as viable options.
Ans: If you are planning to cycle properly, i would suggest aragonite sand. If you want to cut cycling the tank short, i would say go for LS.
VI) I can manage to get 1 Jebao for now, may be add another one after 4-5 months.
Ans: You can skip it for now too if you want, but this is always a welcoming decision to invest in flow.
VII) I will keep FOWLR for at least 2 years, then decide if to add corals or not. In the meantime, I will manage funds for a chiller. So, not thinking of in that line right now.
Ans: Best of luck waiting for 2 years
VIII) Live rocks are enough for bio filtration? Or I need additional bio filter media in sump? In that case I will use another chamber in sump. Do not want to add a mechanical filter. Skimmer can skim out the particles, right
Ans: Wrong. The need for mechanical filtration is already explained in the skimmer section. If you are not willing to make a mechanical section, atleast make sure that the water from the tank drains in "filter socks", the exact micron can be directed towards by xargon/najib.
Before making the sump, do discuss it here and get it seen by xargon/mithun da/najib