I just read today that calcium lactate or gluconate are recommended for their absorbancy.
Their absorbancy is 45% even with low stomach acid, compared to calcium carbonate at only 4%. It also says high doses of calcium causes magnesium deficiency, so the ratio should be 1.2:1 (magnesium to calcium). Liquid supplement is highly recommended.
The presence of fruit juice enhances mineral absorption and retention as it enhances stomach acid... calcium and zinc absorb together in the presence of food... etc.
Side note: 70% of calcium supplements tested were found to be contaminated with lead. Look for no pesticide residues, preservatives , food colouring or sugar.
Also, if you're toxic (autointoxification from pour digestion), then this results in malabsorption. You're right to cleanse. Bowel Cleanse, parasite cleanse and liver cleanse...