As others have said, you need to keep an eye on the levels; given that you used cured LR
, you may not experience a "spike" at all. Many people mistakenly believe that you have to have a spike in ammonia, nitrites, and nitrates in order to cycle your tank. Not true at all. The spike occures, because the number of bacteria initially present in your system are not sufficient to breakdown the waste or organic decay that is occurring. Many people also mistakenly believe that in order to cycle a tank you must use something to provide organic waste or decay (like a live fish or a dead shrimp) again, not true. LR
, especially LR
that is shipped will already provide enough organic decay to begin the cycle of your tank. In your case, buying the rock already cured means that you already have ammonia and nitrite and probably nitrate using bacteria present in the system. The fact that you are reading 0 ammonia and nitrite, but some nitrate tells me that you don't have enough nitrate fixing bacteria in the system. Nitrate fixing bacteria (which are anaerobic) are found in only two places in the marine aquarium: deep in the LR
and in a DSB
(if you have one). Nitrate can also be removed from a system by the use of algae or plants (thus why many people run a refuguim in line with their sump). And of course the use of a protein skimmer will help to cut down on the presence of organic debris in the water in the first place, which will help as well.
The one issue I see with your tank, and it may well be the source of your nitrate issue is the depth of your sandbed. Shallow sandbeds (according to most sources) should be between 3/4" to 1 1/2" deep. Deep sandbed should be between 2 1/2" to 3" or more (some sources suggest as deep as 6") to be effective. Between lies an area of risk; the bed is not deep enough to allow anaerobic bacteria to establish and fix nitrite into nitrate, and yet is too deep to allow organic debris to remain floating in the water column. Thus it becomes trapped and begins to decay adding to your problems and often promoting undesirable algae blooms.
As far as the RO
its a matter of cost effectiveness and convinience. RO
water can be bought today in most supermarkets and lots of LFSs, so spending the $100 to $150 on a unit becomes not a necessity, but a matter of choice. Of course if you are spending $.21 a gallon on water and doing the standard 10 to 20% weekly water changes, you will use a minimum of 40 gallons of water per month @ $.21 or so, thats roughly $8.00/month, and in 12 months, you've spent roughly $96.00. A good RO
unit can be bought for $150.00 + shipping or therearound. OF couse you still have the cost of maintanence (filters etc.) and the additional requirment of monitoring your RO
unit. So again, worth it or not
. As far as should you be using RO
water at minimum, the answer is yes - tap water depending on where you live and filtering system used by your community can have a huge variety of contaminants, from organics (like nitrates and phosphates).
Thats probably way more than you wanted to read, but hope it helps.