Yes your ph is fine where it is now , a neutral 7.0 is going to be your best bet with the fish that we have discussed previously. Also if you just raised the ph a swing of over .2 per day can be hard for some fish to adjust to try bumping is slower in the future , or better use a ph buffer its cheap n easy .
ammonia burns there gills , thus the gasping .
Nitrates are important , but its just veriftcation of your cycle in fw really I can't remember the last time I even looked at n02 or n03 in my fw tanks. I'm not saying it won't hurt the fish , prolonged exposure is bad but the presence of ammonia is the fw fish killer.
I would do bi daily wc if it was me.
Also although it says prime is for ammonia it also will remove nitrates .
The prime is safe to use 5x the dose for your water volume in an emergency detox situation , so use it excess won't hurt.
Also maybe try running ammonia chips instead of carbon.
I run a 50/50 mix in my planned tank because plants make the water tea and the carbon polishes the water , but non planted tanks only get ammo chips.
I use API chips in the cartons 8-10 $ for 5 months worth .
I know from our previous conversations that the tank is mildly fresh but stirring your substrate should not set a mini cycle , if that were the case doing a gravel vac every 3 weeks would do this also.
In fw the beneficial bacteria lives in the water , the filter/bio filter and the sub strate , so IMO , IME unless its just a building up of detrites in the gravel getting back in the water you may need to do more frequent gravel vacs.
If that isn't the case look at other options like your water source.
The fw at my mothers has .25 ammonia out tha tap .
I think the cichlids Will be ok , but wc , wc , wc is all that will detox the water.
Prime bonds on a molecular lvl making it less harmful and easily extracted by plants and filtration but does not make it disappear.
Just because the test can't see it because you changed the molecule .
Is the tank planted ? If not you may consider some fast growing plants such as java moss , its a natural nitrate sponge .
I hope they all make it , let me know if there is anything you need that I can help with.