While gravel vac and substrate cleaning in a shrimp tank are always a point of contention among aquarists and shrimp keepers, we provide our viewpoint here in the hopes that you will be able to determine what is best for your tank.
The general rule most if not every pet store and aquarist advise you get out there is :
Maintain proper filtration and use a Water Changer or Siphon Vacuum Gravel Cleaner once a week to perform a 10% to 20% water change. Use reverse osmosis or deionized water supplemented with Minerals Water Renewal for soft water species.
While this is accurate in most circumstances when having a conventional aquarium, it ignores your bio-load, livestock requirements, and whether or not you have living plants. Leaving aside the type of gravel or substrate you have, of course.
Let us take each point apart and discuss it according to what we see fit in our aquariums.
Conventional Aquarium
Due to the fact that shrimp live to eat, a shrimp aquarium is not like any other aquarium. Most typically used to clear algae and other undesired material in traditional aquariums. This sets us apart from a traditional aquarium, because what is undesirable in a traditional fish aquarium is highly recommended in a shrimp-only aquarium. And by that, I am referring to algae, biofilm, and leftover food.
So, by cleaning your substrate, you are partaking in reducing the amount of food those shrimps need.
Moreover, Shrimps hatch like copepods and they fall in the gravel and inside plants. Being so minute in early days, you can only see them using a microscope. And this leaves us at 99% that you'll be sucking up shrimp larvae without even noticing and with whatever you put on your vacuum intake.
In fact, When having breeding shrimps, it is best not to suck up water at all and only do some water top-offs every few days.
It is only after a week or so, that you can start seeing shrimplets. Those probably you can detect with the naked eye, yet it is still unsafe to do any syphoning on your shrimp only aquarium.
Bio-Load
Shrimps, without a doubt, eat and create waste. However, the waste produced by 100 shrimps is about equal to that produced by one pleco. The waste is then rapidly absorbed by Nitrifying bacteria and live plants, if you have any, therefore you'll have to replenish your plants with nitrogen every few days.
Nevertheless, this being said, doesn't mean that your tank is waste free. You'll most probably have to check your Ammonia, Nitrate and Nitrite every now and then to make sure that the cycle is working properly. And Only then, when your levels spike, it is recommended to do a water change.
Now doing this water change in our opinion, is better achieved with a gravel vac and not a simple hose. WHY? because a gravel vac can be fitted with a net and absorbs the waste under the gravel rather than from the water column. Which is safer than dangling a hose around your tank and absorbing the water from around open spaces.
Live Plants
It's fantastic to have a planted tank. Furthermore, the plants contribute to the oxygenation of the water by absorbing a large amount of undesirable particles and minerals.
That is to say, vacuuming your gravel will remove natural plant fertilizers.
Furthermore, putting mosses or carpeting plants in your tank attracts a large number of shrimps and provides a safe sanctuary for both adult and baby shrimp. They graze on biofilm and algae that have formed on the leaves and roots of plants.
If your goal is to keep shrimp rather than have an attractive aqua-scaping aquarium, vacuuming your gravel becomes less and less vital at this time.
livestock water parameters requirements
When it comes to ornamental shrimps as your sole livestock, different varieties of shrimp, like other tropical fish, have distinct water parameters requirements.
Even if the new water has the same parameters as the old, replacing the water in your tank poses a risk to your shrimps because any little or abrupt change in water quality can cause stress and shedding problems.
As a result, we supplement with minerals and other natural additions, particularly those derived from botanicals and deposits specific to the shrimp species we keep.
However, there is no need to utilize a gravel vac for this; instead, a cup can be used for manual and gradual water refilling. Drop water replenishment is recommended for some species, and if you're going to use a gravel vac, make sure it's designed for nano tanks and has a low suction power.
Substrate
Neutral gravel, lava rock, akadama soil, planting soil... all have different features and benefits depending on the sort of aquarium bottom you have. Each time you vacuum the substrate, you are eliminating part of its characteristics and shortening its lifespan.
Some type of soil, leach ammonia and other elements. However a gravel vac is not going to change this. So when using such type of soil, you'd better be in control and knowing what your doing instead of compensating by doing multiple water changes and vacuuming your gravel.
Filtration
Without going into too much detail on filtration, a UGF or a sponge filter is recommended for most shrimp tanks. These filters are used to maintain the shrimp tank and its residents safe, as well as to change the water parameters in specific circumstances. You're indirectly damaging your filtration system if you change your water frequently. So, the easiest way to describe it is that you should change your water when you clean your filter, not the other way around.
Lessons Learned
Keep water changes to when it's recommended based on your water parameters
Compensate by doing water top-off's
Do a water change when you want to clean your filter
Use a slow syphon and slow drip replenishing system
Use a nano gravel vac under the gravel and not in the water column