Floating aquarium plants and a shrimp-safe fertilizer

Floating plants are the cheapest way to calm down a bright tank. They cut the light, and male bettas and honey gouramis build bubble nests under them. Fry and cherry shrimp hide in the roots. They also take up nitrogen as they grow, and some of it leaves the tank each time you throw extras away.

The catch is that they grow. A cup of red root floaters can cover a 20-gallon in a few weeks under a decent light, and then you are the person with a bucket of spare plants and no takers. That is the good version of the problem. Duckweed is the bad version.

Red root floaters or Amazon frogbit

Red root floaters, Phyllanthus fluitans, have round leaves about half an inch across. Under a strong light with enough iron, the leaves and roots turn red. Under a weak light they stay green. Either way they are easy, and they fit a 10-gallon fine.

Amazon frogbit, Limnobium laevigatum, has bigger, spongy leaves about an inch across and roots that can hang several inches into the water. Fry hide in the roots and shrimp pick at them. Trim the roots when they reach the substrate or block your view.

Both want calm water and dry tops. Water sitting on the leaves makes them rot, so leave an inch or two of air between the surface and the lid, and wipe off condensation if the lid drips onto them.

Salvinia, water lettuce, and duckweed

Salvinia minima has small fuzzy leaves and grows fast. Dwarf water lettuce makes rosettes a few inches wide with long roots, and it needs a bigger tank with an open top or plenty of room under the light. Texas bans every species of salvinia and water lettuce. California, Oregon, and Washington regulate Amazon frogbit. Check your state's list before you order any floater.

Duckweed is the one to keep out. Each frond is a few millimeters long and splits into more, and one frond hiding in a plant order can cover a tank in a month. It sticks to nets, hands, and the filter intake. You can scoop it every day for a year and still find one in the corner.

Never dump spare floaters into a pond, a ditch, or a yard drain. Let them dry out in the sun or bag them for the trash.

Keep them in a ring

Floaters do badly in surface current. A hang-on-back or a spray bar pushes them under, the tops stay wet, and they melt. The current also drags them into the filter intake.

A ring of airline tubing fixes most of that. Cut a length of tubing, join the ends with a straight airline connector, and hold the loop in place with a suction cup clip. Three feet of tubing makes a ring about a foot across, which suits a 20. Put it at the opposite end from the filter return.

Keep part of the surface open no matter what. Bettas and gouramis gulp air at the surface, and you need an open spot to drop food where the fish can find it.

How much to thin, and what they shade

Keep floaters to about half the surface. Most weeks that means scooping out about a third of the mat. A fish net works, or a plastic cup. Take out the oldest and yellowing plants first.

Each plant you throw out takes the nitrogen it used with it. That helps, but it does not replace water changes. The nitrates guide lists plants fifth, after water changes, testing your tap, feeding less, and vacuuming the gravel.

Floaters shade everything under them. Anubias, java fern, and crypts handle it, which is one reason they show up in the low-tech planted tank guide. Carpet plants like Monte Carlo and dwarf hairgrass need strong light at the bottom, and they stall or melt under a full mat. If you have a carpet, keep the ring over the back of the tank.

Feeding floaters in a shrimp tank

Floaters feed from the water, so root tabs do nothing for them. Fish waste covers some nitrogen, but floaters often run short of iron and potassium. Pale new leaves, leaves that shrink with each batch, or red root floaters that stay green under a bright light all point that way.

Copper is the worry in a shrimp tank. Dwarf shrimp do not handle much of it, and many plant fertilizers include a trace as a micronutrient. Seachem says Flourish is safe for shrimp at the normal dose. ThriveS, NilocG's shrimp formula, leaves copper out entirely.

The ThriveS label says 1 ml per 5 gallons, one to three times a week. That is 2 ml in a 10-gallon and 4 ml in a 20-gallon. In a low-light tank, start at once a week, and add a second weekly dose only if new leaves still look pale after three or four weeks. Dose after the weekly water change so you are not siphoning it straight back out.

NilocG also says to add a GH booster if you use soft tap water or RO water. Shrimp need those minerals to molt anyway.

Quarantine floaters before they go in

New floaters bring snails, snail eggs, and duckweed tucked into the roots. They are too delicate for a bleach dip. Float them in a tub of dechlorinated water under a lamp for a week or two and pick through the roots before they reach the display. The plant quarantine guide covers the alum soak if you want a dip that floaters survive.

Shipping is rough on them. A fresh order of red root floaters or frogbit often has a few soft or yellow leaves. Pull those off and expect new growth within a week or two.