I use a Fluval 305 and a TopFin60 HOB filter. I did make the mistake of vacuuming all the gravel all at once a few times.
I have not checked the tap water but I can. I got the Fluval filter used and it already had good bacteria in it. I haven't changed anything in that yet.
I'm not a fan of the top fin but the 305 will handle all the biological filtration you'll need for that tank.
Vaccuuming all your gravel is not a terrible thing to do at all, in fact, it's recommended. Vaccuuming gravel will not remove much beneficial bacteria from the gravel. Maybe 2%. I was more referring to if you had changed out all your gravel or made some other massive change to your tank that could be causing this.
I think the next step is for you to test your tap water directly for ammonia. Also, you should check the pH straight out of the tap as well as testing the pH once the water has been sitting (ie, in a bucket) for 24 hours.
If you want to keep altering the parameters of your water, in order to keep African cichlids, as opposed to keeping fish that are appropriate for a pH in the low 6's, I strongly suggest you get that seachem malawi/victoria buffer. It will not only alter your pH, it will also increase your gH and kH, both of which are important.
pH up (what you used) does nothing to address water hardness. It just increases pH. It's not a smart thing to use long term. The buffer I suggested is.
Just buy the buffer, get a set of measuring teaspoons (1/4, 1/2, full) and measure out how much buffer it takes to get a 5 gallon bucket up to about pH 8 and kH 7-10 (you'll need a kH test kit).
Then, every time you add a bucket of fresh tap water to your tank, dose that bucket with the correct amount of the buffer, and your fish will always be in the same water.
The advice you offered was not the issue, the way you deliver it was.
If you don't tell me more specifically what you think I said wrong, I will continue to be at a loss in terms of understanding what you're referring to. IMO I didn't say anything wrong, and unless somebody points out something specifically that was wrong with what I said, I can't understand where you're coming from.