Hot Tips: Algae Control

A selection of useful tidbits of
information and tricks for the marine aquarist submitted by
Advanced Aquarist’s readership. Readers are encouraged to
post them to our Hot Tips sticky in the
Reefkeeping Discussion
forum or send their tips to
for possible publication. Next
month’s Hot Tip theme will be

Water Purification Tips

Algae Control Tips:

Here’s an strange sounding tip for reducing the time you
spend cleaning algae from the glass: dose sodium silicate to
promote a controlled population of diatoms. Diatoms! I know…
bear with me.

Most aquarist’s introduction to diatoms is as an unsightly
reddish-brown coating of their sand and rocks in the first few
weeks of a new aquarium. At that point, most decide that diatoms
are a “Bad Thing ™” and are forevermore willing to
do anything at all to avoid diatoms or even the possibility of
diatoms. When diatoms are out of balance (like that bloom in a
new aquarium), they don’t do anyone much good. But when
diatom populations are in a stable balance with other processes
in your tank, they are very good for the whole system.


Good things for aquarists might include:

  • Diatoms compete with blue-green algae for resources (#1
    reason to mention this here).
  • Diatoms are much easier to remove from glass and acrylic
    and less unsightly than blue-green algae (light gold tint
    compared to algae’s green blotches).
  • Diatoms are part of “plankton” and just like
    plankton products that you can buy, they provide a healthy
    natural food for filter feeders.
  • Diatoms consume nitrates and phosphates from the water
    column and fix them into their tissue where it can be filtered
    out of your system via your protein skimmer (don’t worry,
    your skimmer won’t get all of them).
  • Diatoms on your sand are some of the best possible food for
    your cleanup crew and are likely to contribute to their
    longevity and increased health/diversity.

Now, how to get them to grow in balance in your aquarium. Diatom
populations in home aquariums are largely limited by available
silica. In order to get more diatoms without getting too many
diatoms, you need to maintain a low but stable level of soluble
silica in your tank water (I seem to get effective results from
1ppm, though I personally haven’t tried concentrations higher
than 1.5ppm).

Before you dose something, you should know your tank needs an
external supply, and you should be able to measure the level to
know where you stand. Hatch makes a good kit for measuring
soluble silica (detection level is .05ppm). To buy soluble
silica, you want to buy the smallest amount of “water
glass” you can buy from your local crafts store. “Water
glass” is sodium silicate and it is used to preserve eggs
(presumably artsy eggs, but I didn’t ask). The smallest I
could buy from the local Michael’s was 1 quart, which is
enough to keep an entire club’s tanks dosed for several

The stuff I bought was 41 baume, which is 29% silica by weight. I
dilute this stuff into a quart of working solution so that each
teaspoon of working solution will dose 10 gallons to a level of
1ppm. It takes 3 3/4 teaspoons of 41 baume solution to make a
quart of working solution, which will treat almost 2000 gallons
to 1ppm. (If you’ve got a tank under 55gal, this is probably
too concentrated to be convenient, so you should probably add 1
1/4 tsp to make a 3x dilute solution and use three times as much
when dosing). This stuff is very alkaline (even more so than
sodium hydroxide — kalkwasser), so use gloves and clean up well.

Once you have your dosing solution mixed up, estimate your total
water volume, which is probably somewhere between 66-80% of the
tank’s total volume, depending on the density of your
rockwork and the depth of your sand. Perhaps a first dose to
0.25ppm, so if your first silica test shows undetectable silica,
divide your volume of water by 40 to determine the number of
teaspoons to add (divide by 13.333 if you made the “small
tank” solution). Always dose into a high-flow area (remember
the alkalinity). I suspect that anything up to 1ppm will be fully
consumed within a week and you’ll probably be at the
detection limit of the hatch kit (0.05ppm) within five days. I
started out testing every other day and found that I have to dose
about 0.33ppm soluble silica each day to maintain a tested level
of 1ppm. Now I only test for silica every month or so along with
my other water quality tests.

If you don’t use RO/DI filtered water, it’s possible that
your water already contains silica (among other things). You need
to take this silica into account when figuring out your dosing
regimen, so having and using a test kit is doubly important for
this case. Many people who find that they have trouble with
diatom blooms are likely to find that their water has very high
silica levels: 18ppm or higher. I recommend removing this from
your water with an effective filter (RO/DI) to prevent blooms and
then adding a precise (and small) amount of silica back to your
tank to encourage balance.

As I said earlier, I maintain 1ppm in my main tank, and that
seems to be the lowest amount that makes the glass scrapings much
easier and the color of the dirty glass more pleasant (I’m
lazy and refuse to scrape more often than weekly). I’ve heard
of people having no blooms with levels up to 3ppm, but I do see a
dusting of diatoms on my sand every few months (not a bloom and
gone within 24 hours, the tiger tail especially loves diatoms)
and am unwilling to raise the silica further without a clear
reason to do so.

Ross (aka rabagley)

In any closed environment with animal life and light you are
going to get plant life. Our tanks are no exception. So the only
choice is whether you get the plant life you like like corraline
algae, macro algae, sea grasses, mangroves, or corals. Or you get
the plant life you don’t like such as hair algae and


Every bit of ammonia, nitrate, phosphate, toxin, heavy metal,
and carbon dioxide consumed or bioaccumulated by plant life you
like is one less bit to feed the plant life you don’t want or
to adversly affect other life you like.

Sure use snails to consume the stuff you don’t, but real
solution is to get plant life you like established and in control
right from that start. That way you will have a tank with the
plant life you desire.

Bob (aka beaslbob)

As long as the speed of phosphate removal is greater than the
speed of production, all nuisance algae will eventually have to
die off, as the phosphates are removed from the sytem.

The two main things that seem to confuse aquarists, are

  1. The resulting die-off of algae takes time
  2. Zero test levels from the water column is not the same as
    zero production, or uptake, of PO4

The aquarist needs to enable the system to dump phosphates
BEFORE they can get used by algae; if 5ppm of PO4 is produced,
and 5ppm uptaken by algae, one will still test a level of zero,
as this only measures ‘excess’ that builds up in the
water column.

The first, easiest way, to eliminate one major source, is via
an RODI unit for water processing.

The second, is to use a phosphate sponge, like phosguard, or

It usually takes a combination of both, to achieve a
‘quicker’ result, though water changes,good skimming,
etc., can achieve the same end,over a longer period of time.


The hobbyists also needs to understand that in addition to the
daily production of PO4 by the life in the system, the phosphates
introduced either via the source water, or livestock
‘surges’ (like when placing an amount of live rock , and
it’s subsequent ‘die-off’ occurs in a system) need to
also be removed.

Since algae require phosphates to grow and thrive, PO4 removal
is not only the true root ‘cure’, it’s also the least
complicated ‘treatment’ around, for dealing with nuisance

Algicides just recycle the PO4 back into the system, to feed
more algae.

‘Clean up crews’ (especially snails) merely recycle
the algae, releasing the PO4 in their poop, to begin the process


I have a little bit of everything:

  • I grow macro algae and harvest them.
  • I have some snails, hermit crabs, urchins, shrimp,
  • I feed my tanks a little bit several time daily – they like
  • I keep my nitrogen sources as close to zero as


I like the combination high in tank circulation and a good
skimmer. The numbers dont mean all that much, but when you can
see detritus, and snail droppings floating around the tank,
instead of to the bottom, you are getting close. In addition a
good cleanup crew will break larger particles of waste down,
making it easier for them to be swept into the water column, and
be removed by the skimmer.


Ask yourself how old your light bulbs are, and replace if


Check your source water! You could be living downstream from a
phosphorous mine and have no clue. Ask your local water district
for the results of their most recent batch of water quality tests
in your area before using tap water in an enclosed system.



  Advanced Aquarist

 Advanced Aquarist

  (103 articles)

Leave a Reply