Heya, welcome back!
Is 3-4 years a common teardown cycle to refresh the substrate?
Yes, especially in a tank with enough light to push plant metabolism into the medium-high to high levels.
This last year has shown significant plant growth slowdown - is that a common failure mode for substrate mineral exhaustion?
Yes. Nutrient exhaustion = slower growth and/or death.
What is the current "best" low-tech/low-maintenance/long-lasting substrate?
There isn't a single "best" substrate specifically for high tech or low tech. In my opinion, Amazonia is THE best substrate for all uses. Substrate properties and nutrient availability are the same across the board, whether high or low tech. Everything else comes down to personal goals/preferences. If you're looking for a more DIY option, then yes, there are mixes that are better than others. My recommendation would be 60% mineralized soil (not raw stuff), 20% calcined clay (such as Turface or Safe T Sorb), and 20% small gravel/coarse sand in the 2-3 mm range. I think Black Diamond makes a suitable product. You'll also want to use this as the cap layer. If you absolutely, positively, cannot mineralize enough soil, at the very least, strain out the coarse stuff with a colander. You really just want the fines. The Turface and sand will provide the needed bulk.
Since these worked well, are you looking to make major changes or improvements during the renovation? If so, what do you want to change?
- Beananimal drain system continued to work well (aside from what I note below), and provide peace of mind if nothing else
- First 3 years, excellent plant growth
- Did not have any issues with gas bubbles causing a mess
- Although it was a pain, the create process was achievable on a budget
- Silicone patching for sump worked perfectly
- The stand has held up just fine - mat used (in lieu of foam) worked just fine, too
- Drilling the glass with ebay diamond holesaws
- Pot scrubbies seem to have done just fine
- Sump design in general seems to have done just fine - aside from the 'fish collection area' being too narrow. That was purely a function of 'run what you brung', i.e. having a 50G to work with.
- External overflow w. minimal internal overflow has been perfect. The triangular gussets might not have been necessary, but definitely gave peace of mind when small children were exploring.
- SCS1200 was a good idea - joints are still perfect
- I stopped using the water conditioner stuff after a while, it didn't seem to make a difference given I was only ever adding 5G to a 150G system.
- Shutting down the tank on my desk, plus the refugium, was a great idea - one tank + sump is plenty for me to deal with (ha, or not deal with)
- The two circulation pumps appear to have done their job well - have never dealt with collections of waste piling up, or dead spots
- The suggestion to add a 1/4" siphon break was most excellent - it continues to work quite well
- The necking-out of the return as it enters the tank (from 3/4" to 1.25" or so) was also a great suggestion
- Peninsula tanks are great. Although this has turned into part of the wall of my office.
Last year, sudden drop-off in plant growth and growth trend became negative
Even though there have been/are tanks that have been going for much longer this sounds like a reasonable timeframe given parts of your system, see above.
Snail population also experienced decline to the point of there being only a few left
Did you have fewer fish to feed?
Fish populations never seemed as stable as I'd expected (or maybe just naive as to fish lifespan
) - some fish lasted 3+ years, others months, suspect that the fairly strong current could also have played a part.
3ish years is a reasonable expectation for most tropical community fish. Make sure to pick fish that are appropriate for your system/current. Rummynose tetras love current and are adapted to it. Angelfish, not so much.
Jungle vals took over (and possibly exhausted the soil?
They're nutrient hogs so that's a strong possibility. They may also have contributed to the declining snail population as they're good at removing Calcium from the water. Did you ever notice thinning or pitting on the snail shells?
Getting fish out of the sump was difficult - better screening up top led to zero fish getting past
1.5" primary siphon drain was (in retrospect) mathematically dumb - primary siphon needed to be 0.75"
1" may be the best compromise. After using 1" drains I won't go back to 0.75" again if the tank size allows for it.
Exposed overflow turned into a cat water dish (not making this up
HAHAHAHA! I laugh out of sympathy. My sump is uncovered, exposed, and easily accessible...
Using 1.5" pool flex hose was dumb, it barely fit, probably puts a ton of unnecessary pressure on glass
I prefer to use regular vinyl hose for at least some sections of my plumbing. Hard PVC plumbing looks great, but it can cause issues with stress too. Having some flexible hose in the mix helps alleviate stress and can improve ease of access.
Too much LED caused some plants to attract that black hair aglae, affected plants were dipped in peroxide, and subsequently died
High light + dissolved organic buildup = BBA. Regular mulm removal (monthly water change?), filter cleaning (!!!!), and CO2 can help a lot. I always recommend CO2 for all plant tanks, even "low tech" as it's so important to plant health. It doesn't really add to maintenance aside from some more frequent trimming and the occasional swap-out, so I still consider it part of a low-maintenance system. Light's the major determinant of "high/low" maintenance as it's what drives the system's metabolism.
Introducing small fish (babies) into an existing fish pecking order = expensive fish food
Been there done that. Includes shrimp.
Substrate at one end might have been too thick (incl. gravel, was ~4")
Go with a 1" (max 1.5") soil mix layer (see above) covered by *at least* 1.5", preferably 2-3", of cap evenly across the tank. If you need more depth, it's better to increase the cap layer than the soil.
Bite the bullet and do monthly water changes - can possibly save a pile of time now that we have a floor drain closer to the tank.
Even if it's only done to remove detritus, this will help out a lot. Adding activated carbon into the filter scheme can help manage unwanted nutrients too. Water changes don't need to be 50%, but the substrate does need to be cleaned of surface junk for optimum health. Just do a light surface suck, there's no need to even put the siphon tube into the substrate. Just remove surface debris.
Pick a fish type and stick with it.
Always a good plan. Livestock need to be planned for just as much as the plants. I can't tell you how many times I had customers come to the store with fish issues due to poor consideration of their stock.
Don't get 'weedy' plants this time - big, moderate-growing maybe?
That's the trade-off. Plants that get big and/or grow extensive root systems come with their own challenges. If you're not supplementing the water, whether though heavy feeding or nutrient additives, then they'll deplete the substrate faster and will create a big mess when being removed. Solutions? Add a substrate amendment such as Osmocote tabs every couple months after the initial six. If you grow swords, removing the outer leaves is a great way of managing size without having to remove the plant. If/when you do need to, use a knife like a cookie cutter to cut the roots around the plant before pulling up. That'll help minimize substrate disturbance.
"Weedy" plants like stems can do just as well as things like Crypts in low maintenance tanks as long as their light needs are met and they're a lot less messy to uproot and replant.
Change up the substrate?
Cover up all plumbing, and don't rush
Don't rush is always a good plan.
Primary siphon gets ripped out and turns into 3/4"
5 year tank refresh cycle, can we do it?
Low maintenance, but monthly or bi-weekly water changes as an attempt to prevent the 3-year die-off
Water changes will help refresh the mineral content of the water, but won't do much to prevent substrate depletion if no nutrients are added as well. The plants have to get their nutrients from somewhere. Regular substrate amendment and adding a water remineralizer such as Equilibrium to give the plants Ca, Mg, K, and Fe will help extend the substrate's effective lifespan; possibly indefinitely.
Spend more time watching it, use it as a teaching aid for our kids.
Hope this helps.