Hi waterdrop,
Thanks again for taking time for another detailed message. Let me try to itemize my issues:
1. I have already contacted Pet Smart, they won't take any fish back, even for free. So, one more time, I am leaning towards your excellent suggestion of perhaps having two shoals of different species; namely Harlequins (6) first, followed by Cardinal tetras (6) when the tank is mature. I definitely want some shrimp in there too and Pet Smart has ghost shrimp apparently, so I will go for it too. I don't know if this is overstocking, so I will need your suggestions on this one, too
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2. I contacted a local CO2 supplier (National Welders, which happens to be a major player in NC, as well) today. It looks like the complete system costs around $200, including a 5 lb full steel cylinder, the regulator and solenoid (the latter two from ebay or DrsF&S). However, the warranty that comes with the regulator/solenoid is only 6 months. In another web site that promoted an electronic regulator, there was a statement about solenoids getting hot and going out of order sometimes in a matter of months. After spending that much of money, it would suck to end up with a broken part. I was also able to make the yeast-based system work better by using fresh ingredients. Plus, the drop checker I received today indicates a CO2 level around 30 ppm so I decided to wait and see at the moment.
3. I have 1 cm laterite and 2-5 cm Eco Complete on top. I was wondering if it would be overkill to further fertilize the plants with the EI method or not. I posted this question in the Planted Tanks section. Assuming the verdict might be a yes, I started wondering if the 0.1% copper in the CSM+B fertilizer would be a hazard for the shrimp. As expected, I posted this question to the inverts forum of course, LOL. I am anticipating that it should be OK, but I just can't help worrying, LOL.
Once again, I would like to thank you for your incredible support during my cycling and afterwards. You are an asset for this forum, trying to help everyone as much as you can.