New guy advice

[Jdig]

Hello. I have a small 20gal tank that I set up as per my LFS. My plan is to keep 1-2 small fish, a shrimp, and some hermit crabs. They provided me with a crushed coral substrate, some fake decorations, and 4 damsels for cycling. I have since discovered this site and now realize I should have used the dead shrimp method and some live rock but I'm 6 weeks into my cycle. My water test levels are: Ammonia 0mg/l, Nitrite 3.3mg/l, Nitrate 110mg/l, ph 7.7, temp 80. Although the ph is low, it appears that my cycle is almost complete and I'm going on vacation for 2 weeks so I'm going to return the damsels to the LFS. I plan on adding some live rock soon. Can I add cured live rock now or should I wait till the nitrites are 0 and I do a water change? I would also like to change my substrate to sand. Can I remove the crushed coral all at once and add the sand or should I change it in small sections as some people have recommended in previous posts. Thanks in advance.

 

[RMPD109]

You can add cured LR anytime to the system. Just be sure it is cured before adding to an established setup. Adding to your setup now will be fine. To change out the CC do as suggested in other posts which is change out 205 of substrate at a time. This allows the new substrate to build the beneficial bacteria needed in the new substrate.