If your max nitrates are 30ppm right before your WC then you might be ok. But as mentioned I keep mine under 20ppm with weekly 50% WC and a deep sand layer will help tremendously. I noticed a little bit of fin rot if I let my nitrates stay above 30 ppm. For haps I recommend larger caves vs the holey rock. While it still works for many hap tank I have large slate where many 2 sided caves of all sizes are created. Most fish prefer caves at or near the bottom of the tank. Your pleco will appreciate this as well. Your females need a place to hide from the males mainly.
A great way to decrease aggression in hap tanks is to shorten your light period. 8 hours is about the max you should really have them on for unless your fish are very mellow and unstressed. When my fish are acting up after I add new tank mates I will cut them back to 4 hours until they mellow out. Also I keep my temps at 78 to keep them mellow. But watch out for ich since it seems flare up at lower temps.
Also to feed your pleco algea wafers use a 1" PVC pipe so you can drop wafers into his hole after the lights go out. My haps ( mainly my 10" venustus) trys to get into the plecos hole and steal wafers so I have to make the cave just right so the pleco can block him out while eating.
When it comes to haps IMO quality of caves is better then quality so get some rocks and mess around until everyone who is beat up has a hiding spot. I'll attach a picture of my 180 gal so you can see how I did my rocks. Haps are generally a mellow fish in the right conditions.
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