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Hi all, while I have had accounts for a variety of forums, I believe this will be my first ever post to any forum, anywhere. I've been exclusively a Facebook hobbyist for years and some of you may know me from there. I assume I can have more than one build thread, I have two tanks, so I'd like to keep separate threads for each. I'll be figuring out the quirks and limitations of forum posting along the way.

I am very much on the cheap end of the hobby, so my 75 (the largest tank I've ever owned) is a basic Aqueon tank from Petco's 50% sale. The stand is made from construction lumber. I'm active in the woodworking hobby as well, though I haven't finished my workbench yet, hopefully this summer...
I used the standard 2x4 design, and I'm never doing it again. 2x4 frames are an extremely inefficient way to utilize the materials and space. Sheet goods are superior, and the cost differences aren't significant. For more information, you'll have to wait for my 10 gallon build thread.

To anyone that is going to make a 2x4 stand (or any DIY stand, tbh), I have two main bits of advice:

1. Use glue. Modern wood glue is stronger than the wood itself. Applying glue to each mating surfaces does more for the strength of the stand than all of the hardware combined. I always viewed glue as being somehow inferior in years past but a quality wood glue is amazing stuff.
2. If you use glue for each surface, and you use good joinery (or faux-joinery, in the case of the corners) to transfer the weight of the tank to the floor without hanging on anything, then you can build the whole thing out of 1x4 and be fine. Go look at commercial stands, whether they be Oase, Waterbox, Petco, whatever, they all use 1x4s and sheet goods. 2x4s are pointless.

I used hardboard facing and paint for a simple finish. The doors were the most difficult bit. At the last minute I decided to inset a bit of plywood for a back, rather than leaving it open, and I'm happy with the decision. It protects the whole stand against racking forces and provides locations for mounting auxiliary equipment.




I applied a black privacy film background, since fish expand their chromatophores in darker environments, resulting in more vivid coloration. I also like the contrast.




Filtration: two canister filters, a SunSun 370 GPH and an Oase Biomaster Thermo 600 (350 GPH) for a total nominal hourly turnover rate of 9.6.
Filter Fittings: Aquario Neo with venturi skimmers, shrimp guards, and lily-type outputs.
CO₂: Two reactors, one on each output, run from a GLA Pro-DS-2 regulator, 5 lb cylinder. I have a flowmeter and pH controller that I'll be installing this summer.
Substrate: Master Soil Next, Powder, Black
Light: Chihiros WRGB II (OG)

This tank was replacing a 16 gallon tank that I had built from a bit of acrylic I had been given. I went ahead and transferred the plants and fish and prepared for the ammonia spike.

The Pogostemon helferi var. 'Downoi' melted to nothing, but there were no other casualties. The ammonia spike came quickly, but my tap water has 0 dKH, so it naturally sits around 6.8. The substrate buffered it further down to 6.0, and with CO₂, down to 5.0. The temperature in the tank is 76°F (24°C). At that temperature and pH, ammonia is extremely non-toxic, it's almost entirely unionized ammonium. Ionized free ammonia tolerance varies by species, but starts to be of concern at about 0.02 mg/L. At 24°C, and 5.0 and 6.0, the Total Ammonia Nitrogen (TAN) reading necessary to yeild 0.02 mg/L of free ammonia is 375 and 40 mg/L, respectively.
So, I didn't worry about the ammonia. I did no water changes, I just let it do its thing, and I lost no fish. The stocking at the time included Sundadanio goblinus, Microdevario kubotai, (two species that are generally considered "sensitive") and an alien Betta.

It took much longer than I had expected for the tank to process the ammonia. I had used the filter media from the 16 gallon predecessor, so I thought it would be over in a week. I hadn't counted on how much phosphate my substrate would devour. I finally set up my auto-doser and mixed salts, and suddenly, my fish were all gasping at the surface. I was confused, I had added lids at the same time and I thought that the lids were blocking the oxygenation of the water. I fiddled with it for a day or two and then tested my water. I finally had nitrites.

I started my foray into the aquarium hobby in Utah in 2012. In all those years, cycling a tank had been simple, though unforgiving. 7.8 pH, 18 dGH, 15 dKH, 350-450 TDS, it was liquid rock. Nitrifiers never experienced nutrient deficiencies and grew rapidly, but ammonia was very toxic, so any little bump in the cycle and fish died. I moved to North Carolina in November of 2020.

Here, the TDS of the tap water is 37. The only thing in our water is the calcium hydroxide (slaked lime) that the water company adds to prevent plumbing corrosion. The pH straight out of the tap is typically 9.5-ish, but it offgasses to 6.8 within 24 hours sitting out, and within seconds of being added to an active tank full of humic, tannic, nitric, and carbonic acids. When the hydroxide offgasses, all that's left is a bit of calcium. I haven't been able to nail down the exact reason, but the API GH test overestimates my hardness significantly. I have good reason to believe that my GH is about 1.5 dGH (all calcium, no magnesium) but the API test always returns 5 dGH. My current running theory is that the API test measures the calcium only (this is actually quite common among GH tests) and then assumes a "normal/average" ratio of calcium and magnesium (1 part calcium to 2 parts magnesium) and therefore can overstate the GH by a factor of 3 if no magnesium is present.

Anyways, that was a bit of a tangent. When I came to North Carolina, I discovered that nitrifiers frequently experience nutrient deficiencies in this incredibly pure water. In particular, phosphate deficiencies. In every tank previously in NC, a bit of fertilizer was all it took, but this was my first experience with an aquasoil devouring my phosphates. It wasn't until my autodoser was adding KH₂PO₄ on a daily basis that my cycle finally got unstuck.

Nitrite poisoning and CO₂ poisoning act the same way, both of them bypass the selective uptake channels and pumps within the gills. They ower the pH of the blood, converting oxygen-carrying hemoglobin into non-oxygen-carrying met-hemoglobin— a condition called methemoglobinemia. It's the same reason benzocaine products like Orajel are no longer approved for use with teething pain in infants, as it can also cause methemoglobinemia (blue-baby syndrome). The Root Effect in fish functions a bit differently than the Bohr Effect in most vertebrates, and again it functions differently in invertebrates that posses cyanoglobin as opposed to hemoglobin.

Anyways, the point is that nitrite poisoning and CO₂ poisoning are additive. So I just turned the CO₂ down for a few days, added some Prime, and watched the fish. I turned it back up once the nitrite portion of the cycle passed, a little less than a week.

And so this was the rather humble start of my 75 gallon journey. I'll try to be less long-winded in my next post bringing it up to its current state.