Let me start by offering the following quote about the zebra's native habitat.
Hypancistrus zebra is native to Brazil. The only reported habitat being on the riverbed of the Rio Xingu, - pronounced Rio Shin-gu). This makes it difficult to re-create the exact conditions and parameters that the fish would normally experience in the wild. Fortunately for us the L46 is relatively adaptable.The Xingu river is a true tributary of the Amazon River, and one which has only recently( in geographical times, 1884) been explored in any great detail. It is made up of three rivers, the Tamitatoaba, the Romero, and the Colisu, which bounds along a series of rapids over 400 miles long. The floor of the xingu is primerily made up of rounded rocks, crevises and a sandy substrate, allowing Hypancistrus zebra to travel throughout it's territory under cover from preditors.
The Amazon and some of its tributaries, called "whitewater" rivers, bear rich sediments and hydrobiological elements. The blackwater and clearwater rivers, such as the Negro, Tapajós, and Xingu have clear or dark water with few nutrients and little sediment. The Xingu is crystal clear and carries little in the way of sediment.
From
zebrapleco.com
Zebras need well oxygenated warm water, smaller ones tend not to tolerate elevated nitrates. The rest is moot in terms of what is required for them to thrive and spawn in aquariums.
Flow: Yes plecos are all pretty much adapted to surviving in some level of current between some of the time and all of the time. However, this doesn't mean they need it to live and thrive. One of the most experienced and accomplished pleco breeders a know keeps all of his plecos in tanks with only sponge filters. There needs to be at least enough flow to keep a tank well oxygenated and to move the debris, However, you can provide more flow if you want and it isn't going to hurt anything. The one consideration when spawning comes into play is to have a tank so arranged that there is current that blows across the mouths of breeding caves rather than into them or from behind them. Of course whatever the type(s) of filtration, it should always be adequate for that tank and bio-load. (I have zebra tanks with sponges and HOBs and some with powerhead driven sponges.)
pH: Pretty much anything from about 6.5 to 8.0 seems to work. In the wild the dry season has a higher level about 6.7 and rainy season a lower level about 6.5. Drops can happen rapidly during the start of the rainy season. (Mine have thrived in 7.1-7.4 pH.) Your 6.8 pH is just fine.
GH/KH/TDS: This is where things get interesting. One of the biggest differences between the dry and rainy seasons is in the TDS (conductivity) of the water. In a nutshell "Absolutely pure water is a poor conductor of electricity." TDS is an expression of conductivity level which measures how much stuff is in the water because the "stuff" conducts electricity. A lot, but not not all, of conductivity comes from what we normally test for using our GH and KH test kits. The Xingu has been tested at about 14 ppm in the rainy season and 80 ppm during the dry- that equated to about a GH of under 1dg to a high of about 4.5dg. The point is they do come from softer water but also from water that is sometimes not super soft the becoming so very rapidly.( I have kept mine in a range of 85ppm to 150ppm roughly GH 4-6 and KH 3-5.)
Temp: Temps can range widely during the year. During the dry season it climbs and can be as high as 90F and then at the onset of the rainy season it can suddenly drop 12+ dg.
The point of all this is that zebras, unlike a lot of fish, thrive on change. Once past the first six or so months they can also tolerate dirtier conditions than many fish. This tends to be true of most Hypancistrus. The can also tolerate sudden parameter changes better than the average fw fish. This is true of pretty much all seasonal spawners,
In terms of tank sizes and layouts. First, I would suggest either a thin layer of larger grained sand or bare bottom. This helps in seeing where food, poop and debris build up. Lots of cover in the form of wood and caves if a minimalist, rocks and a few plants that can stand warm water if you want. (rem- There are no plants for zebras in the wild. (I used to plant my tanks, now they are unplanted, and bare bottom and only lighted during maintenance.)
The more cover you provide, the more zebras you can put into any given space- to a point of course. While you will hear lots of opinions on what size and how many zebras can go into tank X. All I can offer is what I have done successfully.
- 30gal breeder currently holds 11 wild caughts and a few fry. At its peak it was 13 breeders and about 55 assorted fry.
- 20gal long growout currently holds about 33 assorted fry 1.25 to 1.75 inch. Max was about 50.
- 33gal long currently holds 15 about ready to breed F1s along with two adult wc males.
- In the past I had as many as 12 growing out to 2 inch+ in a 10 gal; 30+ .75-1.5 inch in a 15gal.
Small zebras want small spaces, bigger zebras start to want small cave sized spaces. I don't see any problem keeping 3-4 zebras in a 15 gal long term as long as you keep water conditions good. here is certainly no reason you can't have 3-4 3 cm fish in your tank. One cave/fish minimum plus other cover.
Hope this all helps.
