Gravel substrate? Required and if so how much?

[sparkyjf]

Hi all,

Although I've been keeping tropical fish for a number of years (with varying degrees of success!), I have a question that I've never asked for help with and I realise that I don't really understand this topic so would appreciate any advice, answers, opinions and such.

I have a 45l tank which I bought a natural gravel substrate for when I set it up. The gravel was about 3mm in size. I've noticed that the gravel needs regular vacuuming otherwise is builds up a nasty amount of black toxic waste - also I unfortunately put in a bunch of plants without realising they had snails and since this point burrowing snails took hold and have bred uncontrollably in the tank.

I have been considering what to do with the tank to move forwards, and for the time being have removed all of the gravel in order to clean it (of snails if nothing else). I suspect I might replace it with something new entirely.

This leads me to my questions:

1. Is a gravel substrate a requirement? Does it serve an important purpose? I presume it does but I realise I don't actually know!
2. If it is required, how deep should it be (or is there a rule of thumb for how much is suitable for a 45l tank). Or indeed is it just down to aesthetics?

I've found everyone really helpful on this forum and hope you can help me understand this part of tank setup and fish keeping.

Many thanks!

 

[Byron]

Before turning to your specific questions...the increase in snails and the "dirty gravel" are results of the same issue: too high an organic load. The tank size, fish load, fish feeding, and water changes are all factors.

1. Is a gravel substrate a requirement? Does it serve an important purpose? I presume it does but I realise I don't actually know!

Yes. The substrate is the single most important biological component of an aquarium, much more than the filter. The substrate is the primary bacteria bed; many species of bacteria, each performing somewhat different roles, live in the substrate, and some of these cannot live in a filter. Organics accumulate in the substrate, and the bacteria break these down; snails aid this process because they consume all organics (including all fish excrement) and break it down faster for the bacteria to more easily handle. The type of substrate can affect this, which leads to your second question.

2. If it is required, how deep should it be (or is there a rule of thumb for how much is suitable for a 45l tank). Or indeed is it just down to aesthetics?

The grain size of the substrate does impact the bacteria and their handling of the organics. This is why sand is just about the best substrate material, but fine gravel up to pea gravel can also be used. Nothing larger than pea gravel is advisable, and even with pea gravel the organics might get into the substrate as fairly large bits and take longer to be dealt with.

Depth somewhat depends upon plants; large root system plants need the depth. I use play sand in my tanks and have for seven or eight years now, and I tend to have it about 2 inches deep when level, with aquascaping building it a bit deeper in some spots and less along the front for aesthetics. Provided the fish load is not more than the biological system can handle, this works well.

 

[Lilyann]

That said, throughout the years I have ran many discus tanks without substrate/ or with just a very light dusting for ease of cleaning. So, I would not say that substrate is a requirement for a functional bio-filter in an aquarium.
There are caveats, however. You must be very careful of the beneficial bacteria in filter ( using say a canister filter with ample biomedia and a sponge prefilter) and more frequent water changes may be necessary.
In my own experience with these types of systems, water changes are done more regularly. For instance, while growing out juvenile discus I have done water changes daily, sub-adults- every few days, and with adults in a tank without substrate, water changes of 50% every 2 times weekly.

 

[sparkyjf]

Just wanted to thank you both for your input - very helpful and I have cleaned out my old tank and put a fresh new gravel substrate in - all seems to be well so far.