Ok so ive had a 8g bio bfore and 75g reef tank, but this is much more important to me. I plan on keeping multiple frags i this tank. Is a monthly water change adequate, with just frags how much nitrate will actually build up.
I have the same tank with a reef setup. Every coral in my tank is/was a frag. My water parameters are perfect. I would suggest 3 week water changes for a biocube with a protein skimmer, and every 2 weeks for one without. Definitely invest in the protein skimmer. It suppressed algae growth for a good amount of time. As long as you have live sand and plenty of live rock, your nitrate will be fine.
wouldn't hurt to do a water change every 2 weeks - the more you do, the more stable your water conditions. it's really a choice of if you can be bothered or not LOL
3 weeks wouldn't harm them, but 2 might be your better option - even if its 10% each time, every 3 days might be over kill.... it's whatever you can fit into your routine really you just want avoid build up of amm/ites/ates and keep your levels at optimum for everything (im sure you know this already )