New member, first question

I posted a bit about myself in the new member introduction thread, but I'll include some of that info here for background.

I tried my hand at keeping discus about 20 years ago with no success. I was raising German rams at the same time and had great success with breeding pairs. I was also keeping a successful small reef at the time. Due to career demands, I got out of the hobby for about 20 years, but I'm in a good spot now to get back into it so here we go.

I am planning a discus community tank and have a few first questions. The tank is 90 gallons with a 20L sump. The tank is not drilled and I have read a ton of info about the pros and cons of drilling vs not drilling, and I've made up my mind to run an overflow box. I was originally thinking of doing a refugium in the sump and live sword plants in the tank, but then I started seeing all kinds of strong opinions against live plants in a discus tank. I couldn't figure out why people were advising against them. Logic (and science) tells me that live plants will only improve the overall quality if the plants are kept healthy, so why would anyone advise against them?

My next question is about water chemistry. I just bought an API master freshwater kit and a KH/GH kit. My tap water tests at PH-8.4, KH-4, and GH-89.5. I hope I'm reading the chart correctly. I don't have a deionizer or RO machine yet so I can only speculate or wonder about how the water will change once I get that equipment. The aquarium place where I will be getting my fish from tested their PH right in front of me today and it came out at 6.4. They are in the next town over, so it's a different water supply. They said that they use a 50/50 mix of tap water and RO in that tank. Can I expect my PH to come down to around 6.4 by using a 50/50 mix as they do? Also, while I'm on the topic of RO, what is a good RO system that would meet the needs of my 100 gallon system?

So after some more reading I decided to do some more testing to learn what my tap water is doing. I tested the water from my AquaRain ceramic gravity filter and found that the hardness levels are exactly the same as when the water leaves the tap. The PH though was considerably lower at 7.6. I didn't want to believe that the filter had lowered the PH so why was it lower? After further reading I found that aged water can have a lower PH. It's entirely likely that the water in my filter is 24 hours or more old, especially since the filter is pretty much empty. I decided to test the as-yet unfiltered water in the upper chamber of the filter and it too tested at 7.6. So it seems that my tap water drops from 8.4 to 7.6 after sitting for a day or so. That's the good news. The bad news though is that I will be bringing my fish home from 6.4 water and dropping them into 7.4 water. Should I be concerned about this? Further bad news is that I tested my tap water for nitrates and found it at 10ppm. I think the planted sump will help mitigate this problem, but is there anything else I should do, or is 10ppm nothing to stress over?

The first thing that I would recommend is to scrap the API kits, they are less than reliable.

Tap water, in the pipes, doesn't "breathe" thus the pH tends to change once you aerate it. Open your tap fully and let if flow for 5 minutes then collect a small sample and aerate it for 24 hours then test it.

Your tap water mixed with 50% RO will not drop the pH to 6.5, the drop will be minimal

10ppm nitrates in tap water is very annoying and hard to work with, again, check with kits that are not API. If that reading is true then I'd look at RO or keep something other than discus.

I would drill the tank, I'ts an easy DIY job and opens up a world of options. Just google it, go slow and use lots of water when drilling.

From one simply discus forum newbie to another - Welcome.

How are the API kits unreliable? Do they not have reasonable accuracy? What would be considered a reliable test kit?

IMHO......API kits are pretty reliable as are Seachem kits. My electronic meters are not and certainly those dip strips are not. Just my thoughts.

I had always heard that API's were the best. I've never had a problem with the. Here lately people have started saying that they give false results. That's all I know.

Yep, that's me that was bagging API, looks like I'm largely out voted though :)